Category

# Uncategorized

538 items

### Angular Diameter

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The angular diameter or apparent size is an angular measurement describing how large a sphere or circle appears from a given point of view.

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### Bond Clean Price between Regular Coupon Payments

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The clean price of a bond is the value of a bond, excluding accrued interest since issue or the most recent coupon payment.

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### Bond Clean Price between Coupon Payments with a Short First Coupon

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The clean price of a bond is the value of a bond, excluding accrued interest since issue or the most recent coupon payment.

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### Bond Dirty Price between Coupon Payments with a Short First Coupon

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The dirt price of a bond is the value of a bond, including accrued interest since issue or the most recent coupon payment.

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### Bond Dirty Price between Regular Coupon Payments

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The dirt price of a bond is the value of a bond, including accrued interest since issue or the most recent coupon payment.

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### Cyclotron Frequency

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A cyclotron is a type of particle accelerator in which charged particles accelerate outward from the center along a spiral path. The particles are held to a spiral trajectory by a static magnetic field and accelerated...

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### Depth of Field for Photographic Lens

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Depth of field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image.

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### Dividend Discount Model

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The dividend discount model is a method of valuing a company's stock price based on the theory that its stock is worth the sum of all of its future dividend payments, discounted back to their present values.

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### Dolbear's Law

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Dolbear's law states the relationship between the air temperature and the rate at which crickets chirp. As temperatures rise, so does the frequency of chirps.

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### Doppler Redshift

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Doppler redshift is caused by movement of a source away from the observer. The term applies to any increase in wavelength and decrease in frequency caused by relative motion, even outside the visible spectrum.

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### Doppler Shift Frequency Reduction Factor

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The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave (or other periodic event) for an observer moving relative to its source.

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### Doppler Blueshift

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Doppler blueshift is caused by movement of a source toward the observer. The term applies to any decrease in wavelength and increase in frequency caused by relative motion, even outside the visible spectrum.

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### Doyle's Log Rule

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Doyle's log rule describes the volume of wood in a standing tree or log.

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### Drake Equation

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The Drake equation is a probabilistic argument used to arrive at an estimate of the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.

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### Elastic Collision

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An elastic collision is an encounter between two bodies in which the total kinetic energy of the two bodies after the encounter is equal to their total kinetic energy before the encounter. Perfectly elastic collisions...

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### Earthquake Rupture Area

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The rupture area is the area of an earthquake rupture, which is a slip, whether on the surface or beneath, in the Earth's crust that results in a fault and displacement of some sort.

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### Earthquake Downdip Rupture Width

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The downdip rupture width is the average width of a rupture surface measured in the downdip direction.

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### Earthquake Rupture Length

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The rupture length is the length of an earthquake rupture, which is a slip, whether on the surface or beneath, in the Earth's crust that results in a fault and displacement of some sort.

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### Earthquake Fault Slip

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Slip is defined as the relative movement of geological features present on either side of a fault plane, and is a displacement vector. A fault's sense of slip is defined as the relative motion of the rock on each side...

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### Earthquake Fault Slip Rate

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Slip is defined as the relative movement of geological features present on either side of a fault plane, and is a displacement vector. A fault's sense of slip is defined as the relative motion of the rock on each side...

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### Earth Satellite Period in a Circular Orbit

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A circular orbit is the orbit at a fixed distance around any point by an object rotating around a fixed axis. The orbital period is the time it takes the object to revolve around the point, in this case the planet Earth.

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### Eckert Number

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The Eckert number is a dimensionless number used in continuum mechanics. It expresses the relationship between a flow's kinetic energy and the boundary layer enthalpy difference, and is used to characterize heat dissi...

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### Economic Value Added

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Economic value added is an estimate of a firm's economic profit, or the value created in excess of the required return of the company's shareholders. Economic value added is the net profit less the equity cost of the ...

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### Online Advertising Revenue by Visits

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Online advertising revenue is the money brought in by those advertisements with which site visitors interact.

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### Online Advertising Revenue by Impressions

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Online advertising revenue is the money brought in by those advertisements with which site visitors interact.

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### Turkey Portion Counter

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The Turkey Portion Counter calculates the turkey mass needed to feed a group of adults, teenagers and children.

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### Words per Page of a Book

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This formula describes the approximate relationship between pages and words in a book.

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### Words per Page of a Magazine

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This formula describes the approximate relationship between pages and words in a magazine.

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### Words per Page of a Manuscript

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This formula describes the approximate relationship between pages and words in a manuscript.

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### Adiabatic Process Equations for an Ideal Gas

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An adiabatic process is one that occurs without transfer of heat or matter between a thermodynamic system and its surroundings. Energy is transferred only as work.

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### Abbe Number

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The Abbe number, also known as the V-number or constringence of a transparent material, is a measure of the material's dispersion (the variation of refractive index versus wavelength), with high values of V indicating...

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### Allometry Relation for Tree-Trunk Diameter and Height

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Tree allometry establishes quantitative relations between tree-trunk diameter and height.

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### Angle of View

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The angle of view describes the angular extent of a given scene that is imaged by a camera in the vertical and horizontal directions.

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### Angle Subtended

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The angle formed between the bottom and top of an object at a distance from the observer.

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### Anti-Knock Index

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The AntiKnock Index (AKI) or posted octane number (PON) is the headline octane rating shown on the pump in Canada, the United States, Brazil and some other countries.

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### Arc Length on a Circle

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The arc length on a circle is the length of arc, or segment, of the circle.

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### Area of a Regular n-Gon

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A regular n-gon is a plane figure that is bounded by a chain of n straight line segments of equal length closing in a loop to form a closed polygonal chain.

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### Arrhenius Number

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The Arrhenius equation is a formula for the temperature dependence of reaction rates. The Arrhenius number is the exponent for that equation.

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### Average Speed by Displacement

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The speed of an object is the rate of change of its position.

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### Avogadro's Law

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Avogadro's law states that equal volumes of all gases, at the same temperature and pressure, have the same number of molecules. For a given mass of an ideal gas, the volume and amount (moles) of the gas are directly p...

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### Axial Member Deformation

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Axial member deformation is the deformation of the support due to a load along the axis of support.

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### Coulomb's Law

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The magnitude of the electrostatic force of attraction between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between th...

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### Boussinesq Approximation Parameter Using Approximated Gravitational Acceleration

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The Boussinesq approximation is used in the field of buoyancy-driven flow (also known as natural convection). It ignores density differences except where they appear in terms multiplied by the acceleration due to grav...

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### Benjamin Graham Formula

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The Benjamin Graham formula is an intrinsic value formula used to quickly determine how rationally priced stocks were.

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### Bench Stepping

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The step count is the number of steps completed by exercising with bench stepping.

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### Body Mass Index

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The body mass index (BMI), or Quetelet index, is a value derived from the mass (weight) and height of an individual.

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### Baseball Game Score

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Game score in baseball is a metric of the strength of a pitcher in a game with a starting value of 50.

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### Baseball Pythagorean Win Expectancy

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Pythagorean Win Expectancy is an estimate of how many games a team should win based upon runs scored and runs allowed.

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### Baseball Earned Run Average

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The earned run average is the average number of allowed earned runs normalized to the length of a full game.

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### Baseball Runs Created

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Runs created is a baseball statistic used to estimate the number of runs a hitter contributes to his team.

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### Baseball Slugging Percentage

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Slugging percentage (SLG) is a measure of the batting productivity of a hitter,defined as the total bases divided by the number of at bats.

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### Baseball Secondary Average Formula

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Secondary average is a baseball statistic that measures the sum of extra bases gained on hits, walks and stolen bases (less times caught stealing) depicted per at bat. It is a sabermetric measurement of hitting perfor...

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### Baseball Weighted On-Base Average

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The weighted on-base average measures a player's overall offensive contribution per plate appearance.

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### Baseball Isolated Power

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Isolated Power, or ISO, is a sabermetric computation used to measure a batter's raw power by showing how many extra bases a player averages per at bat, defined as slugging percentage minus batting average.

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### Baseball Range Factor

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Range factor is a measurement of a player's fielding, defined as the number of times a player is involved in making an out divided by innings played.

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### Baseball Batting Average on Balls in Play

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The batting average on balls in play is the ratio of hits excluding home runs to at bats excluding strikeouts and homeruns, but including sacrifice flies.

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### Baseball Walks Plus Hits per Inning

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The walks plus hits per inning pitched is a sabermetric measurement of the number of baserunners a pitcher has allowed per inning pitched. It reflects a pitcher's propensity for allowing batters to reach base; therefo...

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### Baseball On-Base Percentage Plus Slugging Percentage

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On-Base Plus Slugging is a single statistic that shows both a batter's ability to get on base and to hit for power, defined as on-base percentage plus slugging percentage.

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### Basketball True Shooting Percentage

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The true shooting percentage is the shooting percentage adjusted for three-pointers and free throws, and measures a player's efficiency at shooting the ball.

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### Basketball Usage Rate

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Usage rate estimates the percentage of a team's possessions a player uses while on the floor.

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### Basketball Effective Field Goal Percentage

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The effective field goal percentage is a statistic that adjusts field goal percentage to account for the fact that three-point field goals count for three points, while field goals only count for two points.

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### Basketball Assist Rate

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The assist rate estimates the percentage of a team's possessions a player assists on while on the floor.

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### Basketball Field Goal Percentage

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Field goal percentage in basketball is the ratio of field goals made to field goals attempted.

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### Beale Number

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The Beale number is a parameter that characterizes the performance of Stirling engines and is often used to estimate the power output of such engines.

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### Beer–Lambert Law With Decadic Absorbance

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The Beer–Lambert law relates the attenuation of light to the properties of the material through which the light is traveling.

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### Beer–Lambert Law with Napierian Absorbance

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The Beer–Lambert law relates the attenuation of light to the properties of the material through which the light is traveling.

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### Bethe Formula

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The Bethe formula describes the mean energy loss per distance traveled of swift-charged particles (protons, alpha particles, atomic ions) traversing matter (or, alternatively, the stopping power of the material).

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### Bicycling Time by Pace

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Pace is the time it takes to cover a certain distance.

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### Bingham Compression Number

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The Bingham compression number expresses the state of a semisolid Bingham material if compressed.

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### Biot Number

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The Biot number is a dimensionless quantity used in heat transfer calculations. It determines whether or not the temperatures inside a body will vary significantly in space, while the body heats or cools over time, fr...

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### Birthday Problem Approximation

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The birthday problem, or birthday paradox, concerns the probability that, in a set of n randomly chosen people, some pair of them will have the same birthday.

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### Blackbody Luminosity of a Sphere

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The blackbody luminosity for a sphere is the total amount of energy emitted by a sphere with uniform temperature in thermal equalibrium with its surroundings.

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### Black Hole Event Horizon Radius

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The event horizon of a black hole is a boundary in spacetime beyond which events cannot affect an outside observer.

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### Black Hole Entropy

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The entropy of a black hole is derived from its effective temperature. The temperature of a black hole is calculated as if the electromagnetic radiation it emits came from a blackbody.

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### Black Hole Temperature

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The temperature of a black hole is calculated as if the electromagnetic radiation it emits came from a blackbody.

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### Black Hole Event Horizon Area

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An event horizon is a boundary in spacetime beyond which events cannot affect an outside observer.

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### Black Hole Lifetime

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A black hole will eventually disappear (or evaporate) due to escaping Hawking radiation. The lifetime of a nonrotating, noncharged Schwarzschild black hole can be derived from the formulas for the Schwarzschild radius...

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### Black Hole Event Horizon Area with Angular Momentum

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An event horizon is a boundary in spacetime beyond which events cannot affect an outside observer.

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### Black Hole Event Horizon Area with Charge

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An event horizon is a boundary in spacetime beyond which events cannot affect an outside observer.

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### Black Hole Radiated Power

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The total radiated power of a black hole comes from Hawking radiation, caused by quantum effects near the event horizon.

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### Black Hole Event Horizon Area with Angular Momentum and Charge

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An event horizon is a boundary in spacetime beyond which events cannot affect an outside observer.

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### Blasius Skin Friction

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A Blasius boundary layer describes the steady two-dimensional laminar boundary layer that forms on a semi-infinite plate, which is held parallel to a constant unidirectional flow. Skin friction is friction between the...

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### Blood Glucose Level from Mean Plasma Glucose Molarity

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The blood sugar concentration or blood glucose level is the amount of glucose (sugar) present in the blood of a human or animal.

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### Bodenstein Number with Thermal Diffusivity

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The Bodenstein number, a dimensionless number that is often used to describe axial mixing in so-called axial-dispersion models for tubular reactors. It represents the ratio between the convective transport to the tran...

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### Bose–Einstein Condensation Temperature for Noninteracting Bosons Using Pressure

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The Bose–Einstein condensation temperature is the temperature at which a free Bose gas transitions to a Bose–Einstein condensate. Under such conditions, a large fraction of bosons occupy the lowest quantum state, at w...

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### Bose–Einstein Distribution for Non-interacting Bosons

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The BoseEinstein distribution describes the occupancy of an energy state within a BoseEinstein condensate.

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### Bose–Einstein Condensation Temperature for Noninteracting Bosons Using Volume

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The Bose–Einstein condensation temperature is the temperature at which a free Bose gas transitions to a Bose–Einstein condensate. Under such conditions, a large fraction of bosons occupy the lowest quantum state, at w...

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### Bose–Einstein Condensation Temperature for Noninteracting Bosons Using Number Density

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The Bose–Einstein condensation temperature is the temperature at which a free Bose gas transitions to a Bose–Einstein condensate. Under such conditions, a large fraction of bosons occupy the lowest quantum state, at w...

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### Boussinesq Number

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The Boussinesq number is a dimensionless number representing the square root of the ratio of inertia force to gravitational force.

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### Boyle Number

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The Boyle number expresses the ratio between the thermodynamic temperature of Boyle's point and the critical temperature.

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### Boyle's Law

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The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system.

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### Bragg's Law

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Bragg's law specifies which angles possess coherent and incoherent scattering from a crystal lattice.

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### Brewster's Angle

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Brewster's angle is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection.

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### Brinell Hardness

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The Brinell scale characterizes the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test piece.

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### Brownell–Katz Number by Bond Number

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The Brownell–Katz number is a combination of capillary number and Bond number.

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### Capital Recovery Factor

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A capital recovery factor is the ratio of a constant annuity to the present value of receiving that annuity for a given length of time.

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### Capital Asset Pricing Model

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The capital asset pricing model is a model used to determine a theoretically appropriate required rate of return of an asset, to make decisions about adding assets to a well-diversified portfolio.

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### Cartesian-to-Polar-Coordinates Equations

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The polar coordinate system is a two-dimensional coordinate system in which each point on a plane is determined by a distance from a reference point and an angle from a reference direction. These can be directly trans...

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### Casimir Effect

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The Casimir effect describes the attractive force between two uncharged, perfectly conducting plates arising from quantum fluctuation effects.

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### Centripetal Acceleration Using Rotation Speed

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Centripetal acceleration is the rate of change of velocity of an object with respect to time as it moves in a circular path.

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### Centripetal Force Using Rotation Speed

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A centripetal force is a force that makes a body follow a curved path. Its direction is always orthogonal to the motion of the body and toward the fixed point of the instantaneous center of curvature of the path.

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### Charles's Law

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Charles's law states that when the pressure on a sample of a dry gas is held constant, the Kelvin temperature and the volume will be directly related.

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### Circle Chord Length by Angle and Radius

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A circle chord is a line segment whose endpoints lie on the circle.

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### Circle Chord Length by Apothem and Sagitta

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A circle chord is a line segment whose endpoints lie on the circle. The sagitta is the distance from the center of the arc bridged by the chord to the center of the chord. The apothem is the distance from the center o...

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### Circle Sector Area

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The area of a sector of a circle depends on the size of that circle and the size of the arc for that sector.

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### Circular Orbit Velocity

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The circular orbit velocity describes the speed of an object in a stable orbit at a fixed distance around another body.

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### Circular Orbit Radius of a Charged Particle in a Magnetic Field

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A charged particle moving in a magnetic field will be pushed into a circular path by the interaction of the charge and the magnetic field. The radius of that path can be calculated from the properties of the charge an...

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### Circumference Formula

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A circle is a simple closed shape in Euclidean geometry. It is the set of all points in a plane that are at a given distance from a given point, the center.

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### Cloud Base Height

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The cloud base is the lowest altitude of the visible portion of the cloud.

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### Cohen's d

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Cohen's d is defined as the difference between two means divided by a standard deviation for the data.

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### Colebrook–White Equation for Darcy–Weisbach Friction Factor

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The Colebrook–White equation expresses the Darcy friction factor as a function of the Reynolds number and pipe relative roughness, fitting the data of experimental studies of turbulent flow in smooth and rough pipes.

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### Colebrook–White Equation for Pipe Roughness

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The Colebrook–White equation expresses the Darcy friction factor as a function of the Reynolds number and pipe relative roughness, fitting the data of experimental studies of turbulent flow in smooth and rough pipes.

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### Combined Gas Law

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The combined gas law states that the ratio between the pressure-volume product and the temperature of a system remains constant.

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### Commodity Contracts Optimal Number

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Calculate the optimal number of contracts to hedge a portfolio

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### Complement Probability

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In probability theory, the complement of any event A is the event [not A], i.e. the event that A does not occur.

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### Compound Annual Growth Rate

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Compound annual growth rate is a business- and investing-specific term for the geometric progression ratio that provides a constant rate of return over the time period.

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### Compton Wavelength

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The Compton wavelength of a particle is equal to the wavelength of a photon whose energy is the same as the mass of the particle.

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### Compton Shift

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Compton scattering is the inelastic scattering of a photon by a charged particle, usually an electron. It results in a decrease in energy (increase in wavelength) of the photon, called the Compton effect. Part of the ...

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### Concave Mirror-Image Equations

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A curved mirror is a mirror with a curved reflecting surface. A concave mirror bulges inward.

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### Concentration to Parts per Million in Water

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Molar concentration is a measure of the concentration of a solute in a solution, or of any chemical species, in terms of the amount of substance in a given volume.

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### Constant Translational Acceleration in a Straight Line

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Constant translational acceleration in a straight line describes the equation of motion of an object moving under constant acceleration along a straight line as a function of time.

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### Constructive Thin-Film Interference

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Thin-film interference is a natural phenomenon in which light waves reflected by the upper and lower boundaries of a thin film interfere with one another, either enhancing or reducing the reflected light. When the thi...

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### Continuous Capital Recovery Factor

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A continuous capital recovery factor is the ratio of a constant annuity to the present value of receiving that annuity for a given length of time compounded continuously.

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### Convex Mirror-Image Equations

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A curved mirror is a mirror with a curved reflecting surface. A convex mirror bulges outward.

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### Corrected QT Interval Using RR Interval

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The QT interval is a measure of the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle. It can be corrected for heart rate for improved detection of patients at increased ri...

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### Corrective Lens Equation for Nearsightedness

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The corrective lens equation for nearsightedness relates the far distance for a person to the necessary lens power to correct it.

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### Corrected QT Interval Using Heart Rate

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The QT interval is a measure of the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle. It can be corrected for heart rate for improved detection of patients at increased ri...

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### Corrective Lens Equation for Farsightedness

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The corrective lens equation for farsightedness relates the comfortable reading distance for a person to the necessary lens power to correct it.

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### Cross-Country Skiing by Pace

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The time spent cross-country skiing equals the skier's pace times distance.

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### Cross-Country Skiing by Speed

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The distance covered cross-country skiing equals the skier's speed times time.

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### Cuboid Volume

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The volume of a cuboid is the quantity of three-dimensional space enclosed by it.

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### Cylinder Total Surface Area

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A cylinder is the surface formed by the points at a fixed distance from a given straight line called the axis of the cylinder. Surface area refers to the area covered by all sides of the cylinder.

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### Cylinder Lateral Surface Area

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A cylinder is the surface formed by the points at a fixed distance from a given straight line called the axis of the cylinder. Lateral surface area refers to the area covered by the curved side of the cylinder.

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### Cylinder Volume

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A cylinder is the surface formed by the points at a fixed distance from a given straight line called the axis of the cylinder. The volume is the space enclosed by the cylinder.

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### Data Transfer Speed

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The data transfer rate is the amount of data that is conveyed per unit of time.

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### Deborah Number

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The Deborah number is a dimensionless number often used in rheology that characterizes the fluidity of materials under specific flow conditions. It is based on the premise that given enough time, even a solid-like mat...

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### De Broglie Frequency by Momentum

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The de Broglie frequency is the frequency associated with a massive particle in motion according to quantum mechanics.

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### De Broglie Wavelength by Kinetic Energy

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The de Broglie wavelength is the wavelength associated with a massive particle in motion according to quantum mechanics.

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### De Broglie Wavelength by Velocity

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The de Broglie wavelength is the wavelength associated with a massive particle in motion according to quantum mechanics.

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### De Broglie Frequency by Velocity

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The de Broglie frequency is the frequency associated with a massive particle in motion according to quantum mechanics.

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### De Broglie Wavelength by Momentum

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The de Broglie wavelength is the wavelength associated with a massive particle in motion according to quantum mechanics.

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### De Broglie Frequency by Kinetic Energy

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The de Broglie frequency is the frequency associated with a massive particle in motion according to quantum mechanics.

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### Decibel-to-Ratio Conversion

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The decibel is a logarithmic unit used to express the ratio of two values of a physical quantity.

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### Destructive Thin-Film Interference

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Thin-film interference is a natural phenomenon in which light waves reflected by the upper and lower boundaries of a thin film interfere with one another, either enhancing or reducing the reflected light. When the thi...

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### Differential Bending of a Bimetallic Strip

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A bimetallic strip is used to convert a temperature change into mechanical displacement. The differential bending of a bimetallic strip describes the radius of curvature as a function of temperature and the length and...

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### Diffraction Grating with Incidence Angle

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A diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams traveling in different directions. The directions of these beams depend on the spacing of th...

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### Diffraction Intensity Ratio for Circular Aperture Diffraction

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The diffraction intensity ratio is the ratio between intensity at a given angle and the incident intensity of light passing through a circular aperture.

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### Diffraction Grating

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A diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams traveling in different directions. The directions of these beams depend on the spacing of th...

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### Dilution Equation with Added Volume

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Dilution is a reduction in the pH of a chemical (gas, vapor, solution). It is the process of decreasing the concentration of a solute in solution, usually simply by mixing with more solvent. To dilute a solution means...

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### Dilution Equation

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Dilution is a reduction in the pH of a chemical (gas, vapor, solution). It is the process of decreasing the concentration of a solute in solution, usually simply by mixing with more solvent. To dilute a solution means...

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### Discounted Security

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A security is a tradable financial asset. A discounted security's rate is based on the redemption value rather than the price.

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### Dittus–Boelter Equation

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The Dittus–Boelter equation (for turbulent flow) is an explicit function for calculating the Nusselt number. The Nusselt number is the ratio of convective to conductive heat transfer across (normal to) the boundary.

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### Doppler-Shifted Frequency

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The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave (or other periodic event) for an observer moving relative to its source.

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### Eccentricity of an Ellipse

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An ellipse is a curve in a plane surrounding two focal points such that the sum of the distances to the two focal points is constant for every point on the curve. The shape of an ellipse (how \"elongated\" it is) is r...

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### Elastic Collision in Two Dimensions Using Incident Angle

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An elastic collision is an encounter between two bodies in which the total kinetic energy of the two bodies after the encounter is equal to their total kinetic energy before the encounter. Perfectly elastic collisions...

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### Elastic Surface Collision

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An elastic surface collision is an encounter between a particle and a surface in which the kinetic energy of the particle after the encounter is equal to the kinetic energy before the encounter. Perfectly elastic coll...

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### Elastic Collision in Two Dimensions Using Impact Parameter

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An elastic collision is an encounter between two bodies in which the total kinetic energy of the two bodies after the encounter is equal to their total kinetic energy before the encounter. Perfectly elastic collisions...

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### Electric Resistivity Formula

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The electrical resistivity is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current.

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### Electromagnetic Skin Depth

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Skin depth is a property of the skin effect, the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, an...

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### Ellipsoid Volume

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An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation.

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### Elliptical Cylinder Volume

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An elliptical cylinder is a cylinder whose cross-section is an ellipse.

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### Elliptical Machine Using Cadence

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An elliptical machine is a stationary exercise machine used to simulate stair climbing, walking or running without causing excessive pressure to the joints, hence decreasing the risk of impact injuries.

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### Elliptical Machine Using Speed

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An elliptical machine is a stationary exercise machine used to simulate stair climbing, walking or running without causing excessive pressure to the joints, hence decreasing the risk of impact injuries.

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### Elliptical Machine Using Pace

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An elliptical machine is a stationary exercise machine used to simulate stair climbing, walking or running without causing excessive pressure to the joints, hence decreasing the risk of impact injuries.

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### Energy Formula for Luminosity

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Luminosity is the total amount of energy emitted by a star, galaxy or other astronomical object per unit time.

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### Energy Efficiency

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Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms.

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### Energy Density of Magnetic Field

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A magnetic field is the magnetic effect of electric currents and magnetic materials. Energy is needed to generate a magnetic field both to work against the electric field that a changing magnetic field creates and cha...

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### Engineering Strain

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Strain is a measure of deformation representing the displacement between particles in the body relative to a reference length.

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### Equation of Motion Using Final and Initial Position

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Equations of motion are equations that describe the behavior of a physical system in terms of its motion as a function of time.

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### Equation of Motion Using Distance

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Equations of motion are equations that describe the behavior of a physical system in terms of its motion as a function of time.

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### Equivalent Sound Level for Fixed Sources

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Sound intensity level is the level of the intensity of a sound relative to a reference value.

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### Equivalent Dose of Ionizing Radiation

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The equivalent dose is a dose quantity representing the stochastic health effects of low levels of ionizing radiation on the human body. Ionizing radiation is radiation that carries enough energy to free electrons fro...

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### Erlang B Formula

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The Erlang B formula determines the probability of packet loss or delay if blocked calls are aborted.

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### Erlang C Formula

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The Erlang C formula determines the probability of packet loss or delay if blocked calls are queued until served.

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### Escape Velocity

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The escape velocity is the minimum speed needed for an object to escape from the gravitational influence of a massive body.

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### Euler Characteristic

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The Euler characteristic is a topological invariant, a number that describes a topological space's shape or structure regardless of the way it is bent.

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### Expanded Boiling-Point Elevation Equation

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Boiling-point elevation describes the phenomenon in which the boiling point of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent...

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### Expected Fielding Independent Pitching

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Expected fielding independent pitching is a measurement of a pitcher's performance that controls for the quality of his team's defense.

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### Exponential Decay

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Exponential decay is the decrease in the amount of a substance at a rate proportional to its current value.

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### Exposure Value

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Exposure value is a number that represents a combination of a camera's shutter speed and f-number, such that all combinations that yield the same exposure have the same exposure value (for any fixed scene luminance).

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### Froude Number

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The Froude number is a dimensionless number defined as the ratio of the flow inertia to the external field (the latter in many applications simply due to gravity).

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### Fabry–Pérot Interferometer Using Finesse Coefficient

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This formula describes the transmission and reflection of light through a FabryPérot interferometer, or etalon, a transparent plate with two reflecting surfaces or two parallel, highly reflecting mirrors.

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### Fabry–Pérot Interferometer Using Plate Reflectance

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This formula describes the transmission and reflection of light through a FabryPérot interferometer, or etalon, a transparent plate with two reflecting surfaces or two parallel, highly reflecting mirrors.

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### Fanno Flow

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Fanno flow describes the adiabatic flow through a constant area duct where the effect of friction is considered.

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### Fermi–Dirac Distribution for Non-interacting Fermions

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The Fermi–Dirac distribution describes how particles are distributed over energy states in systems consisting of many identical particles that obey the Pauli exclusion principle.

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### Fermi Energy for Non-Interacting Fermions

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The Fermi energy is a concept in quantum mechanics usually referring to the energy difference between the highest and lowest occupied single-particle states in a quantum system of non-interacting fermions at absolute ...

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### Fielding Independent Pitching

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Fielding independent pitching is a measurement of a pitcher's performance that controls for the quality of his team's defense.

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### Field of View

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The field of view is the portion of the focused subject visible through the camera lens, assuming a rectilinear lens.

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### First Law of Thermodynamics

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The first law of thermodynamics states that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system minus the amount of work done by the system on its surroundings.

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### First-Order Arrhenius Equation

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The Arrhenius equation is a formula for the temperature dependence of reaction rates.

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### f-Number

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The f-number of an optical system, such as a camera lens, is the ratio of the system's focal length to the diameter of the entrance pupil. It is a quantitative measure of lens speed.

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### f-Number Arithmetic

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The f-number of an optical system, such as a camera lens, is the ratio of the system's focal length to the diameter of the entrance pupil. It is a quantitative measure of lens speed.

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### Football Passer Rating

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The Passer rating is a measure of the performance of passers, primarily quarterbacks, in American football and Canadian football.

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### Force Components

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The force components describe how the force is distrubuted along the x and y axes of a surface.

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### Fourier Number Using Thermal Diffusivity

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The Fourier number is a dimensionless number that characterizes transient heat conduction. Conceptually, it is the ratio of diffusive or conductive transport rate to the quantity storage rate, where the quantity may b...

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### Fourier's Law

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The law of heat conduction, also known as Fourier's law, states that the time rate of heat transfer through a material is proportional to the negative gradient in the temperature and to the area, at right angles to th...

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### Free Water Deficit

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Body water is the water content of an animal body that is contained in the tissues, the blood, the bones and elsewhere. The percentages of body water contained in various fluid compartments add up to total body water.

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### Freezing-Point Depression Equation Using Solvent Properties

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Freezing-point depression is the process in which adding a solute to a solvent decreases the freezing point of the solvent.

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### Freezing-Point Depression Equation Using Cryoscopic Constant

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Freezing-point depression is the process in which adding a solute to a solvent decreases the freezing point of the solvent.

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### Frequency Period Relation

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Frequency is the number of occurrences of a repeating event per unit time. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency.

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### Fresnel Equations for P-Polarized Light

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The Fresnel equations calculate the reflection and transmission coefficients for light incident on an interface between media of differing refractive indices.

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### Fresnel Equations for S-Polarized Light

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The Fresnel equations calculate the reflection and transmission coefficients for light incident on an interface between media of differing refractive indices.

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### Fresnel Number

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The Fresnel number is the difference, expressed in half-wavelengths, between the slant distance from the observation point to the edge of the aperture and the orthogonal distance from the observation point to the cent...

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### Fuel Cost

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The fuel economy of an automobile is the fuel-efficiency relationship between the distance traveled and the amount of fuel consumed by the vehicle.

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### Fuel Used

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The fuel economy of an automobile is the fuel efficiency relationship between the distance traveled and the volume of fuel consumed by the vehicle.

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### Future Value of Annuity

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An annuity is a series of payments made at equal intervals. The future value of an annuity is the accumulated amount, including payments and interest, of a stream of payments made to an interest-bearing account.

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### Future Value of Annuity Due

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An annuity is a series of payments made at equal intervals. An annuity due is an annuity whose payments are made at the beginning of each period. The future value of an annuity due is the accumulated amount, including...

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### Galileo Number Using Characteristic Length

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The Galileo number is proportional to gravity forces divided by viscous forces. The Galileo number is used in viscous flow and thermal expansion calculations—for example, to describe fluid film flow over walls. These ...

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### Galileo Number Using Reynolds Number

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The Galileo number is proportional to gravity forces divided by viscous forces. The Galileo number is used in viscous flow and thermal expansion calculations—for example, to describe fluid film flow over walls. These ...

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### Grashof Number

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The Grashof number is a dimensionless number in fluid dynamics and heat transfer that approximates the ratio of the buoyancy to viscous force acting on a fluid.

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### Gambling Winnings Using American Odds

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The American odds indicate how much money will be won on a $100 wager.

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### Gambling Winnings Using Fractional Odds

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Fractional odds quote the net total that will be paid out to the bettor, should he or she win, relative to the bet.

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### Gambling Winnings Using Decimal Odds

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Decimal odds quote the ratio of the payout amount, including the original bet, to the bet itself.

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### Gas Particles' Velocity

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The thermal velocity or thermal speed is a typical velocity of the thermal motion of particles that make up a gas.

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### Gay–Lussac Number

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The GayLussac number characterizes the relative thermal volume expansion of substances.

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### Gay–Lussac's Law

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The pressure of a gas of fixed mass and fixed volume is directly proportional to the gas's absolute temperature.

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### Glass's δ

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Glass's δ is an estimator of the population effect size that uses only the standard deviation of the second group. An effect size is a quantitative measure of the strength of a phenomenon. A population effect size bas...

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### Goff–Gratch Equation for Ice

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The Goff–Gratch equation is an experimental correlation proposed to estimate the saturation water vapor pressure at a given temperature.

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### Goff–Gratch Equation for Water

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The Goff–Gratch equation is an experimental correlation proposed to estimate the saturation water vapor pressure at a given temperature.

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### Golden Ratio

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Two quantities are in the golden ratio if their ratio is the same as the ratio of their sum to the larger of the two quantities.

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### Graham's Law of Diffusion

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Graham's law of effusion (sometimes called Graham's law of diffusion) states that the rate of effusion of a gas is inversely proportional to the square root of the mass of its particles.

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### Gravitational Redshift

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Gravitational redshift is the process by which electromagnetic radiation originating from a source that is in a gravitational field is reduced in frequency, or redshifted, when observed in a region at a higher gravita...

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### Gravitational Binding Energy of a Uniform Sphere

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The gravitational binding energy is the minimum energy that must be added to a system for the system to cease being in a gravitationally bound state.

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### Gravitational Time Dilation Using Mass

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Gravitational time dilation is a form of time dilation, an actual difference of elapsed time between two events as measured by observers situated at varying distances from a gravitating mass. The higher the gravitatio...

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### Gross Domestic Product Expenditures

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Gross domestic product using the expenditure approach uses the sum of the final uses of goods and services measured in purchasers' prices.

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### Gross Domestic Product Income

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Gross domestic product using the income approach looks at the sum of primary incomes distributed by resident producer units.

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### Gross Domestic Product Production

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The production approach to gross domestic product looks at the value added to goods sold.

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### Hypsometric Equation

Wolfram Research

The hypsometric equation, also known as the thickness equation, relates an atmospheric pressure ratio to the equivalent thickness of an atmospheric layer under the assumptions of constant temperature and gravity.

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### Hohmann Entrance Delta-V

Wolfram Research

The Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits of different radii in the same plane. The entrance delta-v is the change in velocity needed to enter the elliptical orbit.

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### Hazen–Williams Equation

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The Hazen–Williams equation is an empirical relationship that relates the flow of water in a pipe with the physical properties of the pipe and the pressure drop caused by friction.

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### Heat Capacity Ratio Using Specific Heat Capacities

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The heat capacity ratio is the ratio of the heat capacity at constant pressure to heat capacity at constant volume.

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### Heat Capacity Ratio Using Degrees of Freedom

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The heat capacity ratio is the ratio of the heat capacity at constant pressure to heat capacity at constant volume.

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### Heat Engine Efficiency

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A heat engine is a system that converts heat or thermal energy to mechanical energy, which can then be used to do mechanical work.

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### Heat Transfer Coefficient

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The heat transfer coefficient is the proportionality constant between the heat flux and the thermodynamic driving force for the flow of heat.

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### Hedge Effectiveness

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Hedge effectiveness is the extent to which a hedge transaction results in offsetting changes in fair value or cash flow that the transaction was intended to provide (as identified by the hedging entity).

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### Heisenberg Uncertainty Principle for Position and Momentum

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The uncertainty principle, also known as Heisenberg's uncertainty principle or Heisenberg's indeterminacy principle, is any of a variety of mathematical inequalities asserting a fundamental limit to the precision with...

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### Heisenberg Uncertainty Principle for Energy and Time

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The uncertainty principle, also known as Heisenberg's uncertainty principle or Heisenberg's indeterminacy principle, is any of a variety of mathematical inequalities asserting a fundamental limit to the precision with...

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### Helmholtz Resonator Frequency

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Helmholtz resonance is the phenomenon of air resonance in a cavity, such as when one blows across the top of an empty bottle.

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### Henderson–Hasselbalch Equation Using Log Acidity Constant

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The Henderson–Hasselbalch equation describes the derivation of pH as a measure of acidity (using pKa, the negative log of the acid dissociation constant) in biological and chemical systems.

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### Henderson–Hasselbalch Equation Using Acidity Constant

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The Henderson–Hasselbalch equation describes the derivation of pH as a measure of acidity (using pKa, the negative log of the acid dissociation constant) in biological and chemical systems.

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### Heron's Formula

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Heron's formula (sometimes called Hero's formula) gives the area of a triangle by requiring no arbitrary choice of side as base or vertex as origin.

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### Hohmann Exit Delta-V

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The Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits of different radii in the same plane. The exit delta-v is the change in velocity needed to exit the elliptical orbit.

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### Hohmann Angular Alignment

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The Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits of different radii in the same plane. The angular alignment is the bearing needed to make the transfer.

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### Hohmann Transfer Time Using Semimajor Axis

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The Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits of different radii in the same plane. The transfer time is the time it takes to complete the transit along the orbit.

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### Hohmann Total Delta-V

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The Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits of different radii in the same plane. The total delta-v is the change in velocity needed to enter and exit the elliptical ...

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### Hohmann Transfer Time Using Radii

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The Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits of different radii in the same plane. The transfer time is the time it takes to complete the transit along the orbit.

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### Hooke's Law for Potential Energy

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Hooke's law is a principle of physics that states that the force needed to extend or compress a spring by some distance is proportional to that distance.

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### Hooke's Law for Force

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Hooke's law is a principle of physics that states that the force needed to extend or compress a spring by some distance is proportional to that distance.

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### Horizon Distance

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The horizon or skyline is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not.

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### Hyperfocal Distance

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Hyperfocal distance is the nearest focused distance such that the point at infinity still appears sharp.

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### Ideal Gas Law Using Volume

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The ideal gas law is the equation of state of a hypothetical ideal gas. An ideal gas is a theoretical gas composed of many randomly moving point particles whose only interactions are perfectly elastic collisions.

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### Ideal Rocket Equation

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The ideal rocket equation describes the motion of vehicles that follow the basic principle of a rocket: a device that can apply acceleration to itself using thrust by expelling part of its mass with high velocity, and...

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### Illuminance from Luminous Intensity

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Illuminance is the total luminous flux incident on a surface, per unit area.

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### Impulse for Constant Force

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Impulse is the integral of a force, F, over the time interval, t, for which it acts.

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### Inclined Span Catenary Sag

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The inclined span catenary sag describes the tensions and sagging curve, or catenary, of a cable connecting two points at different elevations.

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### Insulin Dose Adjustment for the Day of Westward Travel

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The adjusted insulin dose is the total doses of insulin that a traveler needs to take to account for time zones crossed.

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### Insulin Dose Adjustment for the Day of Eastward Travel

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The adjusted insulin dose is the total doses of insulin that a traveler needs to take to account for time zones crossed.

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### Intensity Ratio for Apparent Magnitude

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The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth.

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### Interest at Maturity Security

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Interest at maturity securities are interest-bearing securities that pay the face amount plus a coupon on the maturity date.

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### Internal Energy of an Ideal Gas Using Particle Number

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The internal energy of a system is the energy contained within the system, excluding the kinetic energy of motion of the system as a whole and the potential energy of the system as a whole due to external force fields...

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### Internal Energy of an Ideal Gas Using Molar Amount

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The internal energy of a system is the energy contained within the system, excluding the kinetic energy of motion of the system as a whole and the potential energy of the system as a whole due to external force fields...

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### International 1/4-Inch Log Rule

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The international 1/4-inch log rule determines the volume of lumber from a log, accounting for the taper that exists in all logs, saw kerf (or the loss of wood as sawdust) and wood removed on the outside of the logs f...

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### Intrinsic Permeability

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Permeability in fluid mechanics and the earth sciences is a measure of the ability of a porous material (often a rock or an unconsolidated material) to allow fluids to pass through it. Intrinsic permeability is permea...

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### Isothermal Process

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An isothermal process is a change of a system in which the temperature remains constant.

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### Kepler's Third Law

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Kepler's laws of planetary motion are three scientific laws describing the motion of planets around the Sun. The third law states that the square of the orbital period of a planet is proportional to the cube of the se...

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### Kepler's First Law

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Kepler's laws of planetary motion are three scientific laws describing the motion of planets around the Sun. The first law states that the orbit of a planet is an ellipse with the Sun at one of the two foci.

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### Kinetic Friction Coefficient

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Kinetic friction is the force resisting the relative motion of solid surfaces sliding against each other.

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### Kinetic Energy

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The kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity.

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### Knoop Hardness

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The Knoop hardness is the measure of the Knoop hardness test, a micro-hardness test for mechanical hardness used particularly for very brittle materials or thin sheets, where only a small indentation may be made for t...

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### Mohr–Coulomb Failure Criterion

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The Mohr–Coulomb failure criterion represents the linear envelope that is obtained from a plot of the shear strength of a material versus the applied normal stress.

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### Larmor Power

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The Larmor formula is used to calculate the total power radiated by a nonrelativistic point charge as it accelerates or decelerates.

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### Law of Cosines

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The law of cosines relates the lengths of the sides of a triangle to the cosine of one of its angles.

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### Law of Haversines

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The haversine formula determines the great-circle distance between two points on a sphere given their longitudes and latitudes.

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### Law of Sines

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The law of sines is an equation relating the lengths of the sides of a triangle (any shape) to the sines of its angles.

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### Law of Tangents

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The law of tangents is a statement about the relationship between the tangents of two angles of a triangle and the lengths of the opposing sides.

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### Lensmaker's Equation

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A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. The lensmaker's equation describes the relationship between focal length and the radii of curvature of the lens.

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### Level Span Catenary Sag

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The level span catenary sag describes the tensions and sagging curve, or catenary, of a cable connecting two points at the same elevation.

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### Logistic Equation

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The logistic equation is used to calculate population growth—the increase in the number of individuals in a population.

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### Log Odds Ratio

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The log odds ratio is a way to quantify how strongly the presence or absence of property A is associated with the presence or absence of property B in a given population.

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### Luminosity Formula for Apparent Magnitude

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Luminosity is the total amount of energy emitted by a star, galaxy or other astronomical object per unit time. The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an...

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### Luminosity Formula for Absolute Magnitude

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Luminosity is the total amount of energy emitted by a star, galaxy or other astronomical object per unit time. Absolute magnitude is a measure of the luminosity of a celestial object on a logarithmic astronomical magn...

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### Macaulay Duration of Bonds

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Modified duration is the name given to the weighted average time until cash flows are received, and is measured in years.

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### Mach Number

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The Mach number is a dimensionless quantity representing the ratio of flow velocity past a boundary to the local speed of sound.

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### Magnetic Reynolds Number

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The magnetic Reynolds number is the magnetic analog of the Reynolds number, a fundamental dimensionless group that occurs in magnetohydrodynamics. It gives an estimate of the relative effects of advection or induction...

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### Mass-Luminosity Relation for Main Sequence Stars

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Luminosity is the total amount of energy emitted by a star, galaxy or other astronomical object per unit time. For stars on the main sequence, luminosity is related to mass.

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### Material Moduli Relationship

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The material moduli relationship describes the relationship between the Young's modulus and the torsion modulus.

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### Maximum Shear Stress in Spring

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The maximum shear stress in a spring is the maximum shear stress the spring can suffer before permanent deformation.

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### Maximum Spring Force

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The maximum spring force is the maximum force the spring can exert before permanent deformation.

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### Meat Defrosting Time in Water

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Thawing time is the time to defrost a food item in a cold-water bath.

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### Meat Defrosting Time in Air

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Thawing time is the time to defrost a food item in the refrigerator.

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### Mechanical Advantage of a Wedge by Angle

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Mechanical advantage is a measure of the force amplification achieved by using a tool, in this case a wedge.

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### Mechanical Advantage of a Lever

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Mechanical advantage is a measure of the force amplification achieved by using a tool, in this case a lever.

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### Mechanical Advantage of a Screw Using Lead

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Mechanical advantage is a measure of the force amplification achieved by using a tool, in this case a screw.

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### Mechanical Advantage of an Inclined Plane by Dimensions

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Mechanical advantage is a measure of the force amplification achieved by using a tool, in this case an inclined plane.

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### Mechanical Advantage of a Wheel and Axle

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Mechanical advantage is a measure of the force amplification achieved by using a tool—in this case, a wheel and axle.

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### Mechanical Advantage of a Screw Using Lead Angle

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Mechanical advantage is a measure of the force amplification achieved by using a tool, in this case a screw.

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### Mechanical Advantage of an Inclined Plane by Slope

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Mechanical advantage is a measure of the force amplification achieved by using a tool, in this case an inclined plane.

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### Mechanical Stress for a Cylinder

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The mechanical stress for a cylinder expresses the internal forces that neighboring particles within the cylinder exert on each other.

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### Mechanical Advantage of a Pulley System

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Mechanical advantage is a measure of the force amplification achieved by using a tool—in this case a pulley system.

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### Mechanical Stresses on a Thin-Walled Hoop

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A cylinder stress is a stress distribution with rotational symmetry, one that remains unchanged if the stressed object is rotated about some fixed axis.

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### Mechanical Stress

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Stress is a physical quantity that expresses the internal forces that neighboring particles of a continuous material exert on each other.

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### Mechanical Advantage of a Wedge by Dimensions

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Mechanical advantage is a measure of the force amplification achieved by using a tool, in this case a wedge.

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### Minimum Power Required to Move Object

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The minimum power required to move an object depends on the work done and the time it takes to complete the movement.

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### Minimum Variance Hedge Ratio

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The hedge ratio compares the value of a position protected through the use of a hedge with the size of the entire position itself. The minimum variance hedge ratio is important when cross-hedging, which aims to minimi...

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### Modified Internal Rate of Return

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The modified internal rate of return is a financial measure of an investment's attractiveness.

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### Modified Duration of Bonds

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Modified duration is the name given to the price sensitivity, and is the percentage change in price for a unit change in yield.

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### Mohr's Circle Plane Normal Strain Y Direction

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Mohr's circle is a two-dimensional graphical representation of the transformation law for the Cauchy stress tensor. Normal strain is a description of deformation in terms of relative displacement of particles in the n...

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### Mohr's Circle Plane Normal Stress X Direction

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Mohr's circle is a two-dimensional graphical representation of the transformation law for the Cauchy stress tensor. Stress is a physical quantity that expresses the internal forces that neighboring particles of a cont...

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### Mohr's Circle Plane Normal Strain X Direction

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Mohr's circle is a two-dimensional graphical representation of the transformation law for the Cauchy stress tensor. Normal strain is a description of deformation in terms of relative displacement of particles in the n...

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### Mohr's Circle Plane Normal Stress Y Direction

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Mohr's circle is a two-dimensional graphical representation of the transformation law for the Cauchy stress tensor. Stress is a physical quantity that expresses the internal forces that neighboring particles of a cont...

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### Mohr's Circle Plane Shear Stress

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Mohr's circle is a two-dimensional graphical representation of the transformation law for the Cauchy stress tensor. Stress is a physical quantity that expresses the internal forces that neighboring particles of a cont...

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### Mohr's Circle Plane Shear Strain

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Mohr's circle is a two-dimensional graphical representation of the transformation law for the Cauchy stress tensor. Strain is a description of deformation in terms of relative displacement of particles in the body tha...

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### Momentum Using Kinetic Energy

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Momentum is the product of the mass and velocity of an object.

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### Momentum Using Velocity

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Momentum is the product of the mass and velocity of an object.

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### Monoprotic Strong Acid-Strong Base Titration

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A monoprotic strong acid–base titration is the determination of the concentration of an acid or base by exactly neutralizing the acid or base with an acid or base of known concentration.

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### Morse Equation

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The Morse equation relates osmotic pressure to solute concentration. Osmotic pressure is the minimum pressure that needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane.

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### Multiple-Slit Diffraction Using Wavenumber

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Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. It is defined as the bending of light around the corners of an obstacle or aperture into the region of geometrical shado...

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### Multiple-Slit Diffraction Using Wavelength

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Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. It is defined as the bending of light around the corners of an obstacle or aperture into the region of the geometrical s...

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### Myth of the Nines Weekly Times

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High availability is a characteristic of a system, which aims to ensure an agreed level of operational performance, usually uptime, for a higher-than-normal period. The nines is a measure of this availability, the rat...

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### Myth of the Nines Monthly Times

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High availability is a characteristic of a system, which aims to ensure an agreed level of operational performance, usually uptime, for a higher-than-normal period. The nines is a measure of this availability, the rat...

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### Myth of the Nines Annual Times

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High availability is a characteristic of a system, which aims to ensure an agreed level of operational performance, usually uptime, for a higher-than-normal period. The nines is a measure of this availability, the rat...

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### Numerical Aperture Using Aperture Diameter

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The numerical aperture of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light.

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### Natural Broadening

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The uncertainty principle relates the lifetime of an excited state (due to spontaneous radiative decay or the Auger process) with the uncertainty of its energy. A short lifetime will have a large energy uncertainty an...

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### Negative Predictive Value

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The negative predictive value is the proportion of negative results in statistics and diagnostic tests that are true negative results.

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### Newton's Second Law

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In an inertial reference frame, the vector sum of the forces on an object is equal to the mass of that object multiplied by the acceleration of the object.

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### Newton's Law of Cooling

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Newton's law of cooling states that the rate of heat loss of a body is directly proportional to the difference in the temperatures between the body and its surroundings, provided the temperature difference is small an...

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### Newton's Law of Universal Gravitation

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Newton's law of universal gravitation states that a particle attracts every other particle in the universe using a force that is directly proportional to the product of their masses and inversely proportional to the s...

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### Nijboer–Zernike Aberration

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An optical aberration is a departure of the performance of an optical system from the predictions of paraxial optics. The analysis by Nijboer and Zernike describes the intensity distribution close to the optimum focal...

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### Nominal-to-Effective Interest Rate

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The effective interest rate is the interest rate on a loan or financial product restated from the nominal interest rate as an interest rate with annual compound interest payable in arrears.

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### Nominal-to-Effective Rate with Continuous Compounding

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The effective interest rate is the interest rate on a loan or financial product restated from the nominal interest rate as an interest rate with annual compound interest payable in arrears.

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### Normalized Frequency

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The normalized frequency, or V number, is a parameter used in optical fibers.

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### Nozzle Air Velocity

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The nozzle air velocity describes the speed of air flowing out of a nozzle under pressure. A nozzle is a device designed to control the direction or characteristics of a fluid flow (especially to increase velocity) as...

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### Numerical Aperture Using f-Number

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The numerical aperture of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light.

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### Nusselt Number

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The Nusselt number is the ratio of convective to conductive heat transfer across (normal to) the boundary.

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### Odds Ratio

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The odds ratio is a way to quantify how strongly the presence or absence of property A is associated with the presence or absence of property B in a given population.

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### Online Advertising Revenue by Hits

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Online advertising revenue is the money brought in by those advertisements with which site visitors interact.

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### Optimal Throwing Angle

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Determine the optimal release angle to maximize distance, assuming no air resistance and a normal Earth-surface gravitational pull using the height of release and the speed of the projectile.

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### Oxygenation Index

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The oxygenation index is a calculation used in intensive care medicine to measure the fraction of inspired oxygen and its usage within the body.

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### Projectile Slant Range

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A projectile is any object thrown into space (empty or not) by the exertion of a force. The projectile slant range describes the final distance of that projectile under the influence of gravity along a nonhorizontal s...

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### Projectile Path

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A projectile is any object thrown into space (empty or not) by the exertion of a force. The projectile path describes the trajectory of that projectile under the influence of gravity.

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### Pooled Standard Deviation

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Pooled standard deviation is the square root of the pooled variance. Pooled variance is a method for estimating the variance of several different populations when the mean of each population may be different, but one ...

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### Page Speed

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The page rate or speed is the rate at which pages of a manuscript are read, spoken or written.

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### Pantoscopic Tilt

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Pantoscopic tilt refers to the frame alignment of a lens in the up-and-down position of the glasses frame.

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### Parallax Distance

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Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semiangle of inclination between those two lines. It can be use...

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### Péclet Number Using Thermal Diffusivity

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The Péclet number is a class of dimensionless numbers relevant in the study of transport phenomena in a continuum. It is defined to be the ratio of the rate of advection of a physical quantity by the flow to the rate ...

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### Perfectly Inelastic Collision

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An inelastic collision is a collision in which kinetic energy is not conserved due to the action of internal friction. A perfectly inelastic collision occurs when the maximum amount of kinetic energy of a system is lo...

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### Perpetuity

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A perpetuity is an annuity in which the periodic payments begin on a fixed date and continue indefinitely.

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### Photon Momentum Using Wavenumber

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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation (such as light) and the force carrier for the electromagnetic force. The momentum of a photon depends on...

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### Photon Energy Using Wavelength

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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation (such as light) and the force carrier for the electromagnetic force. The energy of a photon depends only...

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### Photon Momentum Using Wavelength

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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation (such as light) and the force carrier for the electromagnetic force. The momentum of a photon depends on...

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### Photon Wavenumber Using Wavelength

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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation (such as light) and the force carrier for the electromagnetic force.

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### Photon Energy Using Frequency

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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation (such as light) and the force carrier for the electromagnetic force. The energy of a photon depends only...

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### Photon Momentum Using Frequency

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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation (such as light) and the force carrier for the electromagnetic force. The momentum of a photon depends on...

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### Photon Frequency Using Wavelength

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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation (such as light) and the force carrier for the electromagnetic force.

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### pH Using H+ Concentration

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pH, the potential of hydrogen, is a numeric scale used to specify the acidity or basicity of an aqueous solution.

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### pH Using pOH

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pH, the potential of hydrogen, is a numeric scale used to specify the acidity or basicity of an aqueous solution.

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### pKa Using Concentrations

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An acid dissociation constant is a quantitative measure of the strength of an acid in solution. pKa refers to the logarithm of the acid dissociation constant.

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### pKa Using Acidity Constant

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An acid dissociation constant is a quantitative measure of the strength of an acid in solution. pKa refers to the logarithm of the acid dissociation constant.

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### Planck's Radiation Law Using Frequency

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Planck's law describes the spectral density of electromagnetic radiation emitted by a blackbody in thermal equilibrium at a given temperature.

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### Planck's Radiation Law Using Wavelength

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Planck's law describes the spectral density of electromagnetic radiation emitted by a blackbody in thermal equilibrium at a given temperature.

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### pOH

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pOH, the potential of hydroxide ions, is a numeric scale used to specify the acidity or basicity of an aqueous solution.

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### Poisson Ratio

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Poisson's ratio is the signed ratio of transverse strain to axial strain.

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### Pooled Variance

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Pooled variance is a method for estimating the variance of several different populations when the mean of each population may be different, but one may assume that the variance of each population is the same.

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### Positive Predictive Value

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The positive predictive value is the proportion of positive results in statistics and diagnostic tests that are true positive results.

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### Power Factor Using Electric Apparent Power

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The power factor of an AC electrical power system is defined as the ratio of the real power flowing to the load to the apparent power in the circuit.

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### Prandtl Number Using Thermal Diffusivity

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The Prandtl number is a dimensionless number defined as the ratio of momentum diffusivity to thermal diffusivity.

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### Present and Future Value

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Future value is the value of an asset at a specific date, assuming a certain interest rate or, more generally, rate of return.

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### Present Value of Annuity

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An annuity is a series of payments made at equal intervals. The present value of an annuity is the value of a stream of payments, discounted by the interest rate to account for the fact that payments are being made at...

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### Present and Future Value with Continuous Compounding

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Future value is the value of an asset at a specific date, assuming a certain interest rate, or more generally, rate of return.

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### Present Value of Annuity Due

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An annuity is a series of payments made at equal intervals. An annuity due is an annuity whose payments are made at the beginning of each period. The present value of an annuity is the value of a stream of payments, d...

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### Pressure Formula

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Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed.

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### Prevalence

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Prevalence is the true proportion of a disease in a population.

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### Principal and Interest Using Principal Part

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Principal is the amount on which the issuer pays interest, and which, most commonly, has to be repaid at the end of the term.

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### Principal and Interest Using Interest Part

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Principal is the amount on which the issuer pays interest, and which, most commonly, has to be repaid at the end of the term.

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### Principal Stresses

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At every point in a stressed body, there are at least three planes, called principal planes, with normal vectors, called principal directions, where the corresponding stress vector is perpendicular to the plane, i.e. ...

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### Prism Refraction

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A prism is a transparent optical element with flat, polished surfaces that refract light. At least two of the flat surfaces must have an angle between them, called the apex angle.

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### Probability of Exceedance

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The frequency of exceedance, sometimes called the annual rate of exceedance, is the number of times in a certain period that a random process exceeds some critical value.

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### Probability of the Union of Two Events

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The probability of the union of two events depends on the probability of either event and the probability of only one of the events occuring.

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### Proper Velocity

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Proper velocity, also known as celerity, is an alternative to velocity for measuring motion. Whereas velocity relative to an observer is distance per unit time where both distance and time are measured by the observer...

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### Proper Velocity Using Rapidity

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Proper velocity, also known as celerity, is an alternative to velocity for measuring motion. Whereas velocity relative to an observer is distance per unit time where both distance and time are measured by the observer...

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### Pythagorean Theorem

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The Pythagorean theorem is a fundamental relation in Euclidean geometry among the three sides of a right triangle. It states that the square of the hypotenuse (the side opposite the right angle) is equal to the sum of...

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### Rutherford Scattering Differential Cross-Section

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Rutherford scattering is the elastic scattering of charged particles by the Coulomb interaction.

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### Quadratic Equation

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A quadratic equation is any equation having the form a x^2 + b x + c = 0.

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### Shaking Dog Frequency

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The shaking dog frequency defines a relationship between the mass of a mammal and the rate at which it shakes its body.

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### Rayleigh Number Using Thermal Diffusivity

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The Rayleigh number for a fluid is a dimensionless number associated with buoyancy-driven flow, also known as free convection or natural convection.

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### Radio Horizon Distance

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The horizon or skyline is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. The radio h...

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### RAID Array

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RAID (redundant array of independent disks) is a data storage virtualization technology that combines multiple physical disk drive components into a single logical unit for the purposes of data redundancy, performance...

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### Rainbow Altitude

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A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets, resulting in a spectrum of light appearing in the sky. It takes the form of a multicolored a...

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### Raoult's Law Using Partial Pressures

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Raoult's law is a law of thermodynamics that states that the partial vapor pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its mole fraction...

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### Rapidity

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Rapidity is commonly used as a measure for relativistic velocity. Mathematically, rapidity can be defined as the hyperbolic angle that differentiates two frames of reference in relative motion, each frame being associ...

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### Rayleigh Scattering Cross-Section for Particles

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Rayleigh scattering is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation.

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### Rayleigh Criterion Angle for Circular Aperture Diffraction

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The diffraction intensity ratio is the ratio between intensity at a given angle and the incident intensity of light passing through a circular aperture.

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### Rayleigh Flow

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Rayleigh flow refers to frictionless, nonadiabatic flow through a constant area duct where the effect of heat addition or rejection is considered.

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### Rayleigh Scattering Cross-Section for Molecules of Gases

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Rayleigh scattering is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation.

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### Real Rate of Return

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Rate of return is a profit on an investment over a period of time, expressed as a proportion of the original investment. The real rate of return takes into account the inflation rate.

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### Rectangle Area

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A rectangle is a quadrilateral with four right angles. Its area is the space within its borders.

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### Redlich–Kwong Equation of State

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The Redlich–Kwong equation of state is an empirical, algebraic equation that relates temperature, pressure and volume of gases.

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### Redshift Wavelength

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Redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum.

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### Redshift Frequency

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Redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum.

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### Reduced Mass

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The reduced mass is the \"effective\" inertial mass appearing in the two-body problem of Newtonian mechanics.

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### Reduced and Spectroscopic Wavenumber

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The wavenumber is the spatial frequency of a wave, either in cycles per unit distance or radians per unit distance.

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### Refractive Index

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The refractive index, or index of refraction of a material, is a dimensionless number that describes how light propagates through that medium.

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### Relativistic Energy for Moving Mass

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The energy–momentum relation is the relativistic equation relating any object's rest (intrinsic) mass, total energy and momentum. From this, the relativistic energy can be calculated.

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### Relativistic de Broglie Wavelength by Momentum

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The de Broglie wavelength is the wavelength associated with a massive particle in motion according to quantum mechanics accounting for relativistic effects.

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### Relativistic de Broglie Frequency by Momentum

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The de Broglie frequency is the frequency associated with a massive particle in motion according to quantum mechanics, accounting for relativistic effects.

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### Relativistic Aberration

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Relativistic aberration is the relativistic version of aberration of light for observers who move with velocities close to the speed of light. This causes the rays of light from the source that reach the observer to b...

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### Relativistic Doppler Shift Using Frequency

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The relativistic Doppler effect is the change in frequency of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by the...

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### Relativistic Doppler Shift Using Wavelength and Observer Speed

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The relativistic Doppler effect is the change in the wavelength of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect) when taking into account effects described by...

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### Relativistic Time Dilation

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Time dilation is the phenomenon of a slowing of time as measured by an observer who is traveling at any nonzero velocity relative to the object.

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### Relative Graham Value

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The relative Graham value is a modification of the results of a formula designed by Benjamin Graham for the evaluation of growth stocks.

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### Relativistic Energy for Rest Mass

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The energy–momentum relation is the relativistic equation relating any object's rest (intrinsic) mass, total energy and momentum. From this, the relativistic energy can be calculated.

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### Relativistic de Broglie Frequency by Kinetic Energy

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The de Broglie frequency is the frequency associated with a massive particle in motion according to quantum mechanics, accounting for relativistic effects.

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### Relativistic Redshift

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Redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum. Relativistic redshift is caused by the relative motion of the source...

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### Relativistic Doppler Shift Using Frequency and Observer Speed

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The relativistic Doppler effect is the change in the frequency of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect) when taking into account effects described by ...

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### Relativistic Doppler Shift Using Wavelength

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The relativistic Doppler effect is the change in wavelength of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by th...

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### Relativistic de Broglie Wavelength by Kinetic Energy

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The de Broglie wavelength is the wavelength associated with a massive particle in motion according to quantum mechanics, accounting for relativistic effects.

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### Relativistic Addition of Velocities

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In relativistic physics, a velocity-addition formula is an equation that relates the velocities of objects in different reference frames.

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### Relativistic de Broglie Wavelength by Velocity

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The de Broglie wavelength is the wavelength associated with a massive particle in motion according to quantum mechanics, accounting for relativistic effects.

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### Relativistic de Broglie Frequency by Velocity

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The de Broglie frequency is the frequency associated with a massive particle in motion according to quantum mechanics, accounting for relativistic effects.

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### Relativistic Length Contraction

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Length contraction is the phenomenon of a decrease in length of an object as measured by an observer who is traveling at any nonzero velocity relative to the object.

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### Relativistic Momentum

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The relativistic momentum is the product of the mass and velocity of an object after a Lorentz transformation.

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### Respiratory Quotient

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The respiratory quotient is a dimensionless number used in calculations of basal metabolic rate when estimated from carbon dioxide production. It is calculated from the ratio of carbon dioxide produced by the body to ...

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### Return on Investment

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The return on investment is the benefit to an investor resulting from an investment of some resource.

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### Revised Benjamin Graham Formula

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The Benjamin Graham formula is an intrinsic value formula used to quickly determine how rationally priced stocks were.

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### Reynolds Number Using Kinematic Viscosity

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The Reynolds number is an important dimensionless quantity in fluid mechanics used to help predict flow patterns in different fluid flow situations.

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### Richter Scale Magnitude to Energy

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The Richter magnitude scale assigns a magnitude number to quantify the size of an earthquake. The Richter scale is a base 10 logarithmic scale, which defines magnitude as the logarithm of the ratio of the amplitude of...

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### Richter Scale Magnitude

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The Richter magnitude scale assigns a magnitude number to quantify the size of an earthquake. The Richter scale is a base 10 logarithmic scale, which defines magnitude as the logarithm of the ratio of the amplitude of...

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### Rise and Run of Slopes

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The grade (also called slope, incline, gradient, mainfall, pitch or rise) of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the horizontal.

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### Rolling Friction Coefficient

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Rolling resistance is the force that resists the rolling of a wheel or other circular object along a surface caused by deformations in the object or surface.

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### Rossiter Coefficient and Strouhal Number

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The Rossiter coefficient is related to the Strouhal number, a dimensionless number describing oscillating flow mechanisms. The frequency is the frequency of vortex shedding.

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### Rossiter Coefficient and Frequency

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The Rossiter coefficient is related to the Strouhal number, a dimensionless number describing oscillating flow mechanisms. The frequency is the frequency of vortex shedding.

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### Rowing Machine Using Speed

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An indoor rower, or rowing machine, is a machine used to simulate the action of watercraft rowing for the purpose of exercise or training for rowing.

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### Rowing Machine Using Pace

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An indoor rower, or rowing machine, is a machine used to simulate the action of watercraft rowing for the purpose of exercise or training for rowing.

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### Rule of 70

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The rule of 70 is a method for estimating an investment's doubling time.

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### Running Using Speed

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Running is a method of terrestrial locomotion allowing humans and other animals to move rapidly on foot.

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### Running Using Pace

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Running is a method of terrestrial locomotion allowing humans and other animals to move rapidly on foot.

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### Running in the Rain

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Running in the rain approximates how wet a person would get from running in the rain.

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### Rydberg Formula

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The Rydberg formula is used in atomic physics to describe the wavelengths of spectral lines of many chemical elements.

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### Stopping Distance

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Stopping distance refers to the distance a vehicle will travel from the point when its brakes are fully applied to when it comes to a complete stop. It is primarily affected by the original speed of the vehicle and th...

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### Sackur–Tetrode Equation Using Thermal de Broglie Wavelength

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The Sackur–Tetrode equation is an expression for the entropy of a monatomic classical ideal gas, which incorporates quantum considerations that give a more detailed description of its regime of validity.

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### Sackur–Tetrode Equation Using Internal Energy

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The Sackur–Tetrode equation is an expression for the entropy of a monatomic classical ideal gas, which incorporates quantum considerations that give a more detailed description of its regime of validity.

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### Sample Size for Estimating a Population Mean

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Sample size determination is the act of choosing the number of observations or replicates to include in a statistical sample.

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### Sample Size for Estimating a Binomial Parameter

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The sample size for estimaitng a binomial parameter estimates the minimum sample size to estimate the binomial parameter.

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### Scribner's Log Rule

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Scribner's log rule is a tool for use in the estimation of standing timber volume.

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### Second-Order Arrhenius Equation

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The Arrhenius equation is a formula for the temperature dependence of reaction rates.

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### Seismic Moment Using Rupture Area

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Seismic moment is a quantity used by seismologists to measure the size of an earthquake.

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### Seismic Moment Magnitude and Equivalent Energy

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Seismic moment is a quantity used by seismologists to measure the size of an earthquake. It is directly proportional to the energy released.

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### Seismic Moment Using Rupture Dimensions

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Seismic moment is a quantity used by seismologists to measure the size of an earthquake.

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### Sensitivity

Wolfram Research

Sensitivity (also called the true positives rate) measures the proportion of positives that are correctly identified as such (i.e. the percentage of healthy people who are correctly identified as having the condition).

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### Simple Boiling-Point Elevation Equation

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Boiling-point elevation describes the phenomenon that the boiling point of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent. Th...

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### Simple Interest

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Interest is payment from a borrower or deposit-taking financial institution to a lender or depositor of an amount above repayment of the principal sum (i.e. the amount borrowed). Simple interest is calculated only on ...

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### Single-Slit Diffraction Using Wavenumber and Intensity Ratio

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Singleslit diffraction is when light passes through a narrow slit and creates an interference pattern on the other side.

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### Single-Slit Diffraction Using Wavelength and Rayleigh Criterion Angle

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Singleslit diffraction occurs when light passes through a narrow slit and creates an interference pattern on the other side.

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### Single-Slit Diffraction Using Wavenumber and Rayleigh Criterion Angle

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Singleslit diffraction occurs when light passes through a narrow slit and creates an interference pattern on the other side.

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### Single-Slit Diffraction Using Wavelength and Intensity Ratio

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Singleslit diffraction is when light passes through a narrow slit and creates an interference pattern on the other side.

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### Slant Range to Aircraft

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Slant range is the line-of-sight distance between two points (in this case, one point is an aircraft) that are not at the same level relative to a specific datum.

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### Slope of a Line

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The slope or gradient of a line is a number that describes both the direction and the steepness of the line.

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### Snell's Law

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Snell's law is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media.

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### Sodium Deficit

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Sodium deficit is the measure of the sodium in the patient's blood to the ideal amount.

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### Specific Rotation Using Solution

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Specific rotation is a property of a chiral chemical compound. It is defined as the change in orientation of monochromatic plane-polarized light, per unit distance–concentration product, as the light passes through a ...

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### Specificity

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Specificity (also called the true negative rate) measures the proportion of negatives that are correctly identified as such (i.e. the percentage of healthy people who are correctly identified as not having the conditi...

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### Speed by Initial and Final Values

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The speed of an object is the rate of change of its position.

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### Speed of Sound in an Ideal Gas by Temperature and Mass of Molecule

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The speed of sound is the distance traveled per unit time by a sound wave as it propagates through an elastic medium.

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### Speed of Sound in an Ideal Gas by Temperature and Molar Mass

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The speed of sound is the distance traveled per unit time by a sound wave as it propagates through an elastic medium.

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### Speed under Constant Acceleration

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The speed of an object is the magnitude of its velocity (the rate of change of its position).

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### Spherical Law of Cosines Using Sides

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The spherical law of cosines is a theorem relating the sides and angles of spherical triangles, analogous to the ordinary law of cosines from plane trigonometry.

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### Spherical Law of Sines

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The spherical law of sines is an equation relating the angular lengths of the sides of a triangle (any shape) to the sines of its angles.

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### Spherical Law of Tangents

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The spherical law of tangents is a statement about the relationship between the tangents of two angles of a triangle on a sphere and the angular lengths of the opposing sides.

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### Spherical Law of Cosines Using Angles

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The spherical law of cosines is a theorem relating the sides and angles of spherical triangles, analogous to the ordinary law of cosines from plane trigonometry.

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### Spheroid Volume

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A spheroid is a solid generated by a half-revolution of an ellipse about its major axis (prolate spheroid) or minor axis.

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### Spot Image Size Using Focal Length

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If two objects imaged by a camera are separated by an angle small enough that their Airy disks on the camera detector start overlapping, the objects cannot be clearly separated any more in the image, and they start bl...

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### Spot Image Size Using f-Number

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If two objects imaged by a camera are separated by an angle small enough that their Airy disks on the camera detector start overlapping, the objects cannot be clearly separated any more in the image, and they start bl...

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### Spring Constant for Helical Spring

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The spring constant is the stiffness of a spring—the force needed to stretch it a certian distance.

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### Static Friction Coefficient Using Critical Sliding Angle

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Static friction is a force that opposes the relative lateral motion of two solid non-moving surfaces in contact.

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### Static Friction Coefficient Using Friction Force

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Static friction is a force that opposes the relative lateral motion of two solid non-moving surfaces in contact.

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### Stefan–Boltzmann Law

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The Stefan–Boltzmann law describes the power radiated from a blackbody in terms of its temperature. Specifically, the Stefan–Boltzmann law states that the total energy radiated per unit surface area of a blackbody acr...

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### Stock Contracts Optimal Number

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The optimal futures contracts number is the optimal number of contracts needed to hedge a position. It is calculated by dividing the product of the optimal hedge ratio and the units of the position being hedged by the...

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### Strehl Ratio

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The Strehl ratio is a measure of the quality of optical image formation.

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### Strouhal Number

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The Strouhal number is a dimensionless number describing oscillating flow mechanisms.

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### Subject Magnification

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The subject magnification factor is how much the subject is enlarged.

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### Surface Wave Magnitude Using Distance to Epicenter

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The surface wave magnitude scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements in Rayleigh surface waves that travel primarily along the uppermost...

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### Surface Wave Magnitude Using Epicentral Distance

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The surface wave magnitude scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements in Rayleigh surface waves that travel primarily along the uppermost...

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### Swimming Distance Using Pace

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Swimming distance is the distance covered while a person propels themselves through water or another liquid.

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### Swimming Distance Using Speed

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Swimming distance is distance covered while a person propels themselves through water or another liquid.

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### Torricelli's Theorem

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Torricelli's law, also known as Torricelli's theorem, is a theorem in fluid dynamics relating the speed of fluid flowing out of an orifice to the height of fluid above the opening. The law states that the speed of eff...

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### Telescope Light-Gathering Power

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The light-gathering power of an optical telescope, also referred to as light grasp or aperture gain, is the ability of a telescope to collect a lot more light than the human eye.

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### Telescope Magnifying Power

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The magnification through a telescope magnifies a viewing object while limiting the field of view.

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### Thermal Doppler Broadening of Frequency

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Doppler broadening is the broadening of spectral lines due to the Doppler effect, caused by a distribution of thermal velocities of atoms or molecules.

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### Thermal Deformation

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Thermal deformation refers to any changes in the shape or size of an object due to a change in temperature.

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### Thermal Doppler Broadening of Wavelength

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Doppler broadening is the broadening of spectral lines due to the Doppler effect, caused by a distribution of thermal velocities of atoms or molecules.

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### Thermal de Broglie Wavelength

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The thermal de Broglie wavelength is roughly the average de Broglie wavelength of the gas particles in an ideal gas at the specified temperature.

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### Thermal de Broglie Wavelength for Massive Particles

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The thermal de Broglie wavelength is roughly the average de Broglie wavelength of the gas particles in an ideal gas at the specified temperature.

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### Thermal de Broglie Wavelength for Massless Particles

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The thermal de Broglie wavelength is roughly the average de Broglie wavelength of the gas particles in an ideal gas at the specified temperature.

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### Thermodynamic Energy

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In thermodynamics, the internal energy of a system is the energy contained within the system, excluding the kinetic energy of motion of the system as a whole and the potential energy of the system as a whole due to ex...

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### Thin Lens Equation

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The thin lens formula relates the distances from the object to the lens and from the lens to the image to the focal length for a lens of negligible thickness in air.

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### Tip Calculation

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A tip is a sum of money customarily given by a client or customer to a service worker, in addition to the basic price.

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### Torus Volume

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A torus is a surface of revolution generated by revolving a circle in three-dimensional space about an axis coplanar with the circle. The volume is the space contained within the resulting surface.

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### Total Internal Reflection

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Total internal reflection is the phenomenon that occurs when a propagated wave strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface.

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### Transtubular Potassium Gradient

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The transtubular potassium gradient is an index reflecting the conservation of potassium in the cortical collecting ducts of the kidneys.

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### Trapezoid Area

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A convex quadrilateral with at least one pair of parallel sides is referred to as a trapezoid. The parallel sides are called the bases of the trapezoid, and the other two sides are called the legs or the lateral sides...

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### Triangle Area Using Base and Height

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A triangle is a polygon with three edges and three vertices. The area is the space enclosed by the triangle.

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### Turkey Frying Time

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The turkey frying time is the time needed to properly fry a turkey.

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### Turkey Cooking Time

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The turkey cooking time is the time needed to properly cook a turkey.

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### Two Connected Springs in Parallel

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A spring is an elastic object used to store mechanical energy.

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### Two Connected Springs in Serial

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A spring is an elastic object used to store mechanical energy.

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### Value at Risk

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Value at risk represents the amount of money at risk with a probability of p over a time period t.

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### Van der Waals Equation

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The van der Waals equation is a thermodynamic equation of state that is based on the theory that fluids are composed of particles with nonzero volumes, and subject to a (not necessarily pairwise) interparticle attract...

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### Vector Projection

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The vector projection of a vector a on (or onto) a nonzero vector b (also known as the vector component or vector resolution of a in the direction of b) is the orthogonal projection of a onto a straight line parallel ...

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### Velocity Components

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The velocity of an object is the rate of change of its position with respect to a frame of reference. Its components are the portions of the velocity in the direction of the coordinate system vectors.

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### Vickers Hardness

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The Vickers hardness test was developed as an alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other hardness tests, since the required calculations ...

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### Vis-Viva Equation

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The vis-viva equation, also referred to as the orbital-energy-invariance law, is one of the equations that model the motion of orbiting bodies. It is the direct result of the principle of conservation of mechanical en...

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### Volume of a Solid Sphere

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The volume of a solid sphere is the measure of the space enclosed by it.

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### Weight on Other Bodies

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The weight of an object is usually taken to be the force on the object due to the gravity of a body.

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### Work by Gravity

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A force is said to do work if, when acting, there is a displacement of the point of application in the direction of the force. Work transfers energy from one place to another or from one form to another.

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### Walking Using Speed

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Walking (also known as ambulation) is one of the main gaits of locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an \"inverted pendulum\" gait in which th...

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### Walking Using Pace

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Walking (also known as ambulation) is one of the main gaits of locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an \"inverted pendulum\" gait in which th...

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### Water Hammer Pressure with Slow Closure

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Water hammer (or, more generally, fluid hammer) is a pressure surge or wave caused when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly (momentum change). A...

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### Wave Propagation in Strings

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The velocity of propagation of a wave in a string is proportional to the square root of the force of tension of the string, and inversely proportional to the square root of the linear density of the string.

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### Wave Speed Using Period

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The phase velocity of a wave is the rate at which the phase of the wave propagates in space.

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### Wave Speed Using Frequency

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The phase velocity of a wave is the rate at which the phase of the wave propagates in space.

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### Weighted Average Cost of Capital

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The weighted average cost of capital is the rate that a company is expected to pay on average to all its security holders to finance its assets.

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### Wien Displacement Law for Peak Frequency

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Wien's displacement law states that the blackbody radiation curve for different temperatures peaks at a wavelength inversely proportional to the temperature. The shift of that peak is a direct consequence of the Planc...

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### Wien Displacement Law for Peak Wavelength

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Wien's displacement law states that the blackbody radiation curve for different temperatures peaks at a wavelength inversely proportional to the temperature. The shift of that peak is a direct consequence of the Planc...

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### Word Rate

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The word rate is the speed at which words are written.

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### Words per Page of a Screenplay

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This formula describes the approximate relationship between pages and words in a screenplay.

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### Work by Torque

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A force is said to do work if, when acting, there is a displacement of the point of application in the direction of the force. Work transfers energy from one place to another or from one form to another.

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### Work by Force

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A force is said to do work if, when acting, there is a displacement of the point of application in the direction of the force. Work transfers energy from one place to another or from one form to another.

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### Work by Force at an Angle

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### Work by Acceleration and Distance

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### Young's Modulus

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Young's modulus, also known as the elastic modulus, is a measure of the stiffness of a solid material. It is a mechanical property of linear elastic solid materials. It defines the relationship between stress (force p...

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### Zeiss Formula

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The Zeiss formula is a supposed formula for computing a circle of confusion criterion for depth-of-field calculations.