Question

what is Stokes law in physics ​

Answer 1

In 1851 george gabriel stokes derived an

expression an now nown as stokes law for the frictional force also called drag force exerted on spherical objects with very small reynolds numbers in a viscous fluid .

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Answer 2

Answer:

In 1851, George Gabriel Stokes derived an expression, now known as Stokes' law, for the frictional force – also called drag force – exerted on spherical objects with very small Reynolds numbers in a viscous fluid.[1] Stokes' law is derived by solving the Stokes flow limit for small Reynolds numbers of the Navier–Stokes equations.

Explanation:

The force of viscosity on a small sphere moving through a viscous fluid is given by:[3]

{\displaystyle F_{d}=6\pi \,\mu \,R\,v\,} {\displaystyle F_{d}=6\pi \,\mu \,R\,v\,}

where:

Fd is the frictional force – known as Stokes' drag – acting on the interface between the fluid and the particle

μ is the dynamic viscosity (some authors use the symbol η)

R is the radius of the spherical object

v is the flow velocity relative to the object.

In SI units, Fd is given in newtons (= kg m s−2), μ in Pa·s (= kg m−1 s−1), R in meters, and v in m/s.

Stokes' law makes the following assumptions for the behavior of a particle in a fluid:

Laminar flow

Spherical particles

Homogeneous (uniform in composition) material

Smooth surfaces

Particles do not interfere with each other.

Note that for molecules Stokes' law is used to define their Stokes radius.

The CGS unit of kinematic viscosity was named "stokes" after his work.

Stokes' law is the basis of the falling-sphere viscometer, in which the fluid is stationary in a vertical glass tube. A sphere of known size and density is allowed to descend through the liquid. If correctly selected, it reaches terminal velocity, which can be measured by the time it takes to pass two marks on the tube. Electronic sensing can be used for opaque fluids. Knowing the terminal velocity, the size and density of the sphere, and the density of the liquid, Stokes' law can be used to calculate the viscosity of the fluid. A series of steel ball bearings of different diameters are normally used in the classic experiment to improve the accuracy of the calculation. The school experiment uses glycerine or golden syrup as the fluid, and the technique is used industrially to check the viscosity of fluids used in processes. Several school experiments often involve varying the temperature and/or concentration of the substances used in order to demonstrate the effects this has on the viscosity. Industrial methods include many different oils, and polymer liquids such as solutions.

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