A small rigid sphere of radius r moves with speed v through a viscous liquid in the creeping-flow regime where Stokes' law is valid. What is the magnitude of the viscous drag?
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Question

A small rigid sphere of radius r moves with speed v through a viscous liquid in the creeping-flow regime where Stokes' law is valid. What is the magnitude of the viscous drag?

G1 Physics · Accepted Answer

For slow motion of a sphere through a viscous liquid at very low Reynolds number, Stokes' law gives F(viscous) = 6πηrv. The drag is proportional to viscosity η, sphere radius r, and speed v. Correct option: A.