Question

(Experiments in which iron beads exercise on rails)

Without any friction between the iron beads and the rails, the mechanical energy will be perfectly preserved, making the starting height and the last reaching height equal. However, it is said that the mechanical energy is preserved even if the friction between the iron beads and the rails is large enough. Why is that?

Answer 1

Without any friction between the iron beads and the rails, the mechanical energy will be perfectly preserved, making the starting height and the last reaching height equal. However, it is said that the mechanical energy is preserved even if the friction between the iron beads and the rails is large enough.

This is because when friction between iron beads and rail is large enough, no sleeping will be there.ie, the point of contact of iron beads and rail is at rest (lowest point on bead which is contact with rail is at rest.). This means point at which friction force is acting is at rest.

Therefore work done by frictional force is zero.

Thus mechanical energy perfectly preserved when friction is large enough.