Homework Solution

TQ 9-15

The finger initially located closest to the center of the meter stick supports more of the weight of the meter stick than the finger initially further from the center.

Therefore, the normal force exerted on the finger by the stick is greatest on the finger located closest to the center of the stick and the force of static friction (when lateral motion of the fingers is attempted) is greatest on this same finger.

Applying a lateral force inward force on both fingers results in the finger further from the center moving since the static friction force on it is less.

The far finger will stop moving when the force of kinetic friction acting on it becomes larger (as the finger moves inward the normal force increases) than the static friction force on the other. At this point the finger that was initially farther from the center is now nearer to the center and the other finger moves.