PURPOSE: To show that the instantaneous velocity of an object executing uniform circular motion is tangent to the circle.

DESCRIPTION: A pool ball is rolled clockwise around the inside of the circular band. When the ball leaves the end of the circular segment it will travel in the direction tangent to the circle at the point where it leaves. Click your mouse on the photograph above to see a video of the action.

SUGGESTIONS: Suggest three possibilities: (1) the ball will tend to move away from the center of the circle, (3) the ball will tend to continue to move around in a circle, or (2) the ball will move away tangent to the circle. Let your students vote before doing the experiment.

See Question of the Week #82 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA 1D55.10) See also Demonstration D1-31: TRAJECTORY FROM SPIRAL.

EQUIPMENT: Circular band and pool ball.

SETUP TIME: 10 minutes.

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