Using this equation, along with other well-known principles of physics, one can write an
expression that describes the rate at which the sphere falls through a quiescent, viscous fluid.
The drag force (Fd), acts upward just like friction. Along with it the buoyancy force (Fb), the
thrust exerted by the liquid on the sphere also acts upward. The two forces acting upward are
balanced by the weight of the sphere. Figure-1 shows a pictorial representation of the various
forces acting on the sphere falling through the liquid