PhysicsLAB: Centripetal Force

Refer to the following information for the next two questions.

A rock tied to a post moves in a circle at constant speed on a frictionless horizontal surface. All the forces acting on the rock are shown: Tension T, support force n by the table, and the force due to gravity W.

The vector responsible for circular motion is

The net force on the rock is

Refer to the following information for the next four questions.

In this case the rock is tied to a string and swings in a circular path as shown. It is not resting on a surface. No friction. Use the parallelogram rule and find the resultant of vectors T and W.

What is the direction of the resultant of T and W?

Does this resultant lie in the plane of the circular path?

Is this resultant also the horizontal component of T?

Is the resultant T + W (that is, the horizontal component of T) the centripetal force?

Refer to the following information for the next three questions.

In the case shown below, the rock rides on a horizontal disk that rotates at constant speed about its vertical axis (dotted line). Friction prevents the rock from sliding.

Which force is centripetal?

Which force provides the net force?

Why do we not say that the net force is zero?

Refer to the following information for the next two questions.

Now the rock is held in place by friction against the inside wall of the rotating drum.

Which force is centripetal?

Which force provides the net force?

Refer to the following information for the next question.

More challenging! This time the rock rests against the frictionless inside wall of a cone. It moves with the cone, which rotates about its vertical axis (dotted line). The rock does not slide up or down in the cone as it rotates.

Should the resultant force lie in the plane of the circular path? Why?