Concepts

Circular motion, centripetal forces

Overview

A weight is attached to the end of the string. The weight moves up and down depending on the period of rotation of the ball on the other end of the string. When the ball spins with a certain period, the weight reaches equilibrium. Note: the ball and weight are visible in a large lecture hall, but the alligator clip is not.

Details

Equipment

• [1] Tennis ball on a string threaded through a glass tube
• [1] Alligator clip
• [1] 200 g mass

Classroom Assembly

1. Attach the 200 g mass to the end of the string and place it on the table.
2. Adjust the string so that the distance between the weight and the glass tube is approximately 6".
3. Attach the alligator clip above the weight at the base of the glass tube. The alligator clip will act as a reference to show how far the weight has moved.

Important Notes

• Practice this demo in advance. Smooth motion is required.

Script

1. Holding the glass tube vertically, begin to spin the ball.
2. Lift the weight from the table while you are spinning the ball. The weight will move up or down depending on the period of rotation of the ball.
3. Adjust the period of the ball until the alligator clip has returned to the base of the glass tube.

Additional Resources