Stokes' law

 Stokes' law is a formula that describes the relationship between the drag force acting on a spherical particle moving through a fluid and the particle's velocity. It is often used to calculate the terminal velocity of a small spherical particle moving through a viscous fluid.

The formula for Stokes' law is:

F = 6πηrv

where: F = the drag force acting on the particle η = the viscosity of the fluid r = the radius of the particle v = the velocity of the particle

Stokes' law makes the following assumptions:

1. The fluid is incompressible and homogeneous.
2. The flow is laminar, which means that there is no turbulence.
3. The particle is spherical and small enough that the fluid flow around it is not disturbed.
4. The particle's velocity is constant and not changing direction.
5. The particle is moving slowly enough that the fluid flow around it is not affected by any disturbances caused by the particle's motion.
6. The fluid is at rest at infinity (i.e., far away from the particle).

Stokes' law is an important tool for understanding the behavior of small particles in fluids and is commonly used in fields such as engineering, physics, and chemistry. However, it is important to note that it is only applicable under certain conditions, and that in real-world situations, the behavior of particles in fluids can be much more complex