Question

A certain front-loading washing machine has a drum of diameter 25.2 inches. A small tennis ball placed inside spins in a vertical circle pressed against the inner wall of the drum. How quickly would the drum have to spin (in radians per second) in order to ensure that the tennis ball remained pinned against the wall for the entire cycle without falling off?

Answer 1

There will be two forces acting on the tennis ball- gravitational force and the centrifugal force.

Centrifugal force acts radially outwards, only when the ball is at the top most position in the circle, centrifugal force will act directly opposite to the gravitational force. At all other points in the circle centifugal force acts at an angle to the gravitational force. If the centrifugal force is enough at the top most point to keep the ball in place then it will be enough at all other points as well to ensure the circular motion.

Force of gravity,

Centrifugal force is,

diameter = 25.2 inches = 0.64 m

radius = 0.32m