Question

What is the direction of the force that acts on clothes in the spin cycle of a washing machine?

a. outward
b. inward
c. up
d. down

Answer 1

a. outward

Answer 2

This is poorly worded question because you need to think carefully about your frame of reference. If you were a piece of clothing inside the machine, rotating with it, then there would indeed seem to be an outward force. This is centrifugal force. People say that this force is fictitious because it doesn't exist if you look from outside of the washing machine.

In an inertial frame of reference where the machine is stationary but the drum is spinning, the only forces on the clothes are from gravity, the paddles on the drum going round and round, and a reaction force from the sides of the drum.

Gravity is obviously downwards, the force from the paddles points all over the place, but the reaction from the drum points consistently inwards.

This I would say the answer is either a, or b+d depending on your frame of reference

Answer 3

Since the motion is circular and uniform, the net force must be directed inward.