Yay for Slow Moving Spheres!

­­­­Let me tell you a story, boys and girls, about one Sir George Stokes.

He came up with a mathematical description of the reactionary force that works against a sphere moving through an inactive, viscous fluid at a low velocity. (Very exciting, I know.)

His law; Stokes' Law is written as: Fd = 6πμrv

• Fd is the drag force of the fluid on a sphere.
• μ is the fluids viscosity.
• v is the velocity of the sphere.
• r is the radius of the sphere

While Stokes’ Law is straight forward, it is subject to some limitations. Specifically, this relationship is valid only for laminar flow. Laminar flow is defined as a condition where fluid particles move along in smooth paths in fluid layers gliding over one another. This means his expression only works for as the title states; for slow moving spheres, as a fast object would not travel with laminar flow and a sphere is only relevant as the expression requires a radius.

What I'm trying to say is it's not very relevant in most situations. Luckily, good old Stokes is better known for other works. (Why I did not cover them, I do not know!)