- To provide an example of Newton's First Law.
- To demonstrate the direction of centripetal force.
Place the appatatus on an OHP. Place the ball at position A of Figure 1. Tell the class that you plan on flicking the ball causing it to roll in a circular path as defined by the retaining wall. Have the class decide which way the ball will roll when it reaches the gap.
Flick the ball and observe its path. Describe the direction of force exerted by the wall on the ball while in contact, i.e., perpendicular to the wall toward the center, and how Newton's first law explains the ball's path (straight line) once the ball is free of the wall.