In an experiment with a block of wood on an inclined plane, the following observ

Question

In an experiment with a block of wood on an inclined plane, the following observations are made: (1) If the block is placed on the inclined plane, it remains there at rest. (2) If the block is given a small push, it accelerates towards the bottom without any further pushing. What conclusion can be drawn?

a. The coefficient of kinetic friction must be negative.
b. The coefficients of kinetic friction and static friction
c. The coefficient of kinetic friction is larger than the coefficient o
d. The coefficient of static friction is larger than the coefficient of kinetic friction.
e. The coefficient of static friction is zero and the coefficient of kinetic friction is
non-zero.

I know the answer is D, but why is it not C? I just want to clarify this conceptually!

Thanks!

Explanation / Answer

d. The coefficient of static friction is larger than the coefficient of kinetic friction.

It is always true and c is incorrect as kinetic friction coefficient will never be larger than that of static friction

It takes more energy to get something moving than to keep it moving.

This is because everything has a sort of inertia. Everything wants to maintain an equilibrium. When you get something moving, you are breaking that equilibrium. To keep something moving, well, you've already set an equilibrium. There is still friction, but that is because of the shape of the molecules and their density. And it is much less than static friction.

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