# When is stokes law valid

## When can you use Stokes law?

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.

## What are the limitations of Stokes law?

When the solid content of a suspension is high, Stokes’ equation may not show the real sedimentation rate. High solid content imparts additional viscosity to the system, which must be taken into consideration if the correct rate of settling is to be determined. The equation contains only the viscosity of the medium.

## What are the four conditions of Stokes law?

1) The law applies to a fluid of infinite extent . 2) The law does not hold good if the spherical body is moving so fast that conditions are not streamline. 3) The spherical body must be rigid and smooth .

## What is Stoke’s law in physics?

noun Physics.

the law that the force that retards a sphere moving through a viscous fluid is directly proportional to the velocity of the sphere, the radius of the sphere, and the viscosity of the fluid. the law that the frequency of luminescence induced by radiation is usually less than the frequency of the radiation.

## What is the formula for Stokes law?

He found what has become known as Stokes’ Law: the drag force F on a sphere of radius a moving through a fluid of viscosity η at speed v is given by: … F=6πaηv. Note that this drag force is directly proportional to the radius.

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## What is unit of viscosity?

The SI unit for dynamic viscosity η is the Pascal-second (Pa-s), which corresponds to the force (N) per unit area (m2) divided by the rate of shear (s-1). Just as in the definition of viscosity!

## How is viscosity calculated?

There are several formulas and equations to calculate viscosity, the most common of which is Viscosity = (2 x (ball density – liquid density) x g x a^2) ÷ (9 x v), where g = acceleration due to gravity = 9.8 m/s^2, a = radius of ball bearing, and v = velocity of ball bearing through liquid.

## What is Stokes law and terminal velocity?

Stokes’ law shows that the frictional drag (F) is directly proportional to the weight of the sphere; in other words F is proportional to r3. The formula for viscosity shows that the terminal velocity (v) is proportional to the radius squared; v is greater for a larger sphere than for a smaller one of the same material.

## What is Terminal Velocity in viscosity?

Terminal velocity is the maximum speed an object achieves while falling through a fluid. 1. When you drop something, gravity pulls it down while the viscosity of the fluid pushes back up. At first, the force of gravity is stronger than the resistance, and the object accelerates.

## What is the viscosity of water?

The dynamic viscosity of water is 8.90 × 10−4 Pa·s or 8.90 × 10−3 dyn·s/cm2 or 0.890 cP at about 25 °C. Water has a viscosity of 0.0091 poise at 25 °C, or 1 centipoise at 20 °C.

## What is critical velocity?

: the greatest velocity with which a fluid can flow through a given conduit without becoming turbulent.

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## What forces act on the ball while falling in a viscous stationary medium?

Figure 2. There are three forces acting on an object falling through a viscous fluid: its weight w, the viscous drag FV, and the buoyant force FB.

## What is a Stokes?

(Units) the cgs unit of kinematic viscosity, equal to the viscosity of a fluid in poise divided by its density in grams per cubic centimetre. 1 stokes is equivalent to 10–4 square metre per second. Symbol: St. [C20: named after Sir George Stokes (1819–1903), British physicist]

## What is terminal velocity in physics?

Terminal velocity, steady speed achieved by an object freely falling through a gas or liquid. … An object dropped from rest will increase its speed until it reaches terminal velocity; an object forced to move faster than its terminal velocity will, upon release, slow down to this constant velocity.