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# Engineering

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### Dean Number

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The Dean number is a dimensionless group in fluid mechanics, which occurs in the study of flow in curved pipes and channels.

### 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.

### Differential Gear Ratio

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The gear ratio is the relationship between the engine angular frequency and the angular frequency of the vehicle's wheels.

### Doyle's Log Rule

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

### Drag Coefficient

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The drag coefficient is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water.

### Ekman Number

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The Ekman number is a dimensionless number used in fluid dynamics to describe the ratio of viscous forces to Coriolis forces.

### 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...

### Archimedes Number

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The Archimedes number is used to determine the motion of fluids due to density differences. It is a dimensionless number defined as the ratio of external forces to internal viscous forces.

### 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...

### Acceleration Number

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The acceleration number characterizes acceleration flow.

### Accelerating Frequency

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Fluid dynamic accelerating frequency

### Albedo

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Albedo is a measure for reflectance or optical brightness.

### Alfvén Number

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The Alfvén number describes the relative scale for phenomena within an Alfvén wave, a type of magnetohydrodynamic wave in which ions oscillate in response to a restoring force provided by an effective tension on the m...

### 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.

### 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.

### Atwood Number

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The Atwood number is a dimensionless number in fluid dynamics used in the study of hydrodynamic instabilities in density-stratified flows.

### Bond Number

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The Bond number, or Eötvös number, is a dimensionless number measuring the importance of gravitational forces compared to surface tension forces, and is used to characterize the shape of bubbles or drops moving in a s...

### Boussinesq Approximation Parameter Using Fluid Densities

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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...

### 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...

### Bagnold Number

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The Bagnold number is the ratio of grain collision stresses to viscous fluid stresses in a granular flow with interstitial Newtonian fluid.

### 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.

### Bejan Number for Heat Transfer

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The Bejan number is the dimensionless pressure drop along a channel of length L.

### Bingham Compression Number

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

### 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...

### 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...

### Bodenstein Number with Thermal Conductivity

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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...

### 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.

### Boyle Number

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

### 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.

### Brinkman Number

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The Brinkman number is a dimensionless number related to heat conduction from a wall to a flowing viscous fluid, commonly used in polymer processing.

### Brinkman Rheological Number

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The Brinkman number is a dimensionless number related to heat conduction from a wall to a flowing viscous fluid, commonly used in polymer processing.

### Brownell–Katz Number by Viscosity

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

### Brownell–Katz Number by Bond Number

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

### Bulk Concentration

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The bulk concentration describes the ratio of suspended particles to the fluid as a whole.

### Capillary Number

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The capillary number represents the relative effect of viscous forces versus surface tension acting across an interface between a liquid and a gas, or between two immiscible liquids.

### Cauchy Number

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The Cauchy number is a dimensionless number in continuum mechanics used in the study of compressible flows.

### Centrifugal Pump Power

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Centrifugal pump power describes the power of a certain class of pumps used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow.

### Chandrasekhar Number

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The Chandrasekhar number is a dimensionless quantity used in magnetic convection to represent the ratio of the Lorentz force to the viscosity.

### 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.

### 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.

### Data Transfer Speed

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

### 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...

### 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.

### 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.

### 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.

### Erlang B Formula

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

### 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.

### Eötvös Number

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The Eötvös number, also called the Bond number, is a dimensionless number measuring the importance of gravitational forces compared to surface tension forces, and is used (together with the Morton number) to character...

### 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).

### 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).

### 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.

### First Cowling Number

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The Cowling number expresses the magnetic-to-inertia forces ratio.

### First Euler Number Using Friction Force

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The Euler number is a dimensionless number used in fluid flow calculations. It expresses the relationship between a local pressure drop caused by a restriction and the kinetic energy per volume of the flow, and is use...

### First Euler Number Using Pressure Difference

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The Euler number is a dimensionless number used in fluid flow calculations. It expresses the relationship between a local pressure drop caused by a restriction and the kinetic energy per volume of the flow, and is use...

### First Knudsen Number

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The Knudsen number is a dimensionless number defined as the ratio of the molecular mean free path length to a representative physical length scale.

### 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.

### 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.

### 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...

### Fourier Number for Mass Transfer

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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...

### Fourier Number Using Thermal Conductivity

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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...

### 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...

### 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 ...

### 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 ...

### 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.

### Gay–Lussac Number

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

### Graetz Number

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The Graetz number is a dimensionless number that characterizes laminar flow in a conduit.

### Hartmann Number

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The Hartmann number, related to the Chandrasekhar number, is a dimensionless quantity used in magnetic convection to represent the ratio of the Lorentz force to the viscosity.

### Hyperfocal Distance

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

### Indicated Horsepower

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Indicated horsepower is the theoretical power produced in a reciprocating engine if it is completely frictionless in converting the expanding gas energy in the cylinders.

### 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...

### 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...

### Lewis Number Using Thermal Diffusivity

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The Lewis number is a dimensionless number defined as the ratio of thermal diffusivity to mass diffusivity. It is used to characterize fluid flows where there is simultaneous heat and mass transfer.

### Lewis Number Using Thermal Conductivity

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The Lewis number is a dimensionless number defined as the ratio of thermal diffusivity to mass diffusivity. It is used to characterize fluid flows where there is simultaneous heat and mass transfer.

### Lift Coefficient

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The lift coefficient is a dimensionless coefficient that relates the lift generated by a lifting body to the fluid density around the body, the fluid velocity and an associated reference area.

### Lorentz Number

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The Lorentz number is a dimensionless number that relates the thermal conductivity of a metal to its temperature and its electrical conductivity.

### 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.

### 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...

### Maximum Stable Sand Castle Height

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A sand castle is a type of sand sculpture resembling a miniature building. Its height depends on a number of factors, such as the shape, size and mixture of the sand grains, the moisture content and the details of the...

### Moment of Inertia Ratio

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The moment of inertia ratio is the ratio of the actual moment of inertia to an object's inertia if it were a point mass.

### 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...

### 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...

### 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...

### 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.

### 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...

### Normalized Frequency

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

### 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.

### Nusselt Number

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

### 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.

### Péclet Number for Mass Transfer

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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 ...

### 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 ...

### Prandtl Number Using Thermal Conductivity

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

### 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.

### 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.

### Rayleigh Number Using Thermal Conductivity

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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.

### 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...

### 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.

### Reynolds Number Using Dynamic 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.

### 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.

### Richardson Number

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The Richardson number is the dimensionless number that expresses the ratio of the buoyancy term to the flow shear term.

### Rossby Number

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The Rossby number is a dimensionless number used in describing fluid flow.

### 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...

### Schmidt Number Using Kinematic Viscosity

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The Schmidt number is a dimensionless number defined as the ratio of momentum diffusivity (kinematic viscosity) and mass diffusivity, and is used to characterize fluid flows in which there are simultaneous momentum an...

### Schmidt Number Using Dynamic Viscosity

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The Schmidt number is a dimensionless number defined as the ratio of momentum diffusivity (kinematic viscosity) and mass diffusivity, and is used to characterize fluid flows in which there are simultaneous momentum an...

### Scribner's Log Rule

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

### Second Cowling Number

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The Cowling number expresses the magnetic-to-intertia forces ratio.

### 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.

### 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...

### 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...

### Stanton Number

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The Stanton number is a dimensionless number that measures the ratio of heat transferred into a fluid to the thermal capacity of fluid.

### Strouhal Number

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

### Subject Magnification

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

### Suratman Number

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The Suratman number is a dimensionless number used in the characterization of free-surface fluid dynamics. It represents a ratio of surface tension to the momentum transport (especially dissipation) inside a fluid.

### Swelling Interface Number

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The swelling interface number is important in describing the relationship between solvent penetration and solute diffusion.

### 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 ...

### Weber Number

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The Weber number is a dimensionless number in fluid mechanics that is often useful in analyzing fluid flows where there is an interface between two different fluids, especially for multiphase flows with strongly curve...

### Wind Turbine Power

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A wind turbine is a device that converts the wind's kinetic energy into electrical energy.

### 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.