Demos: 1D-08 Ball in Ring

A circular ring containing a gap is placed on the overhead projector. A steel ball is made to roll around the inside circumference of the ring. When the ball leaves the ring through the gap, it continues in a straight line, illustrating that a force is needed to keep the ball moving in a circle.

Directions: Place the ring on the overhead stage and adjust the focus. Start the ball moving near the gap so that it will travel the full length of the ring before emerging at the gap.

Suggestions for Presentation: Pose a problem to the class. If the ball is moving in a circle and it emerges from the circle, what will its path be after it leaves the gap? Many students believe that it will continue in a circular path. Before repeating the demo, draw a straight line on the overhead along the path that the ball will take.

Applications: Reference to other demos showing that when the central force is removed, the object continues in a straight line, according to Newton’s First Law.

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