Demonstrates conservation of energy and shows how the transformation of mechanical energy doesn’t depend on mass. The instructor can also discuss circular motion, explaining why the ball doesn’t fall off the track at the top of the loop. In addition, the instructor can offer the problem to the students to determine the minimum height for the ball to complete the loop without falling or sliding.
The image above shows the behaviour of the ball when released from three different heights H1, H2, & H3. Only H3 takes into consideration kinetic energies associated with both linear and rotational motions of the ball.
Two identical loop tracks are available for demonstration. When they are carefully aligned, the ball will jump from one track to another. It will not reach its original height (there are losses due to friction), but it will go around the loop of the second track.
- Solid white ball
- Larger ball: 1.75″ diameter, 42 g.
- Smaller ball: 1.0″ diameter, 10 g.
- One or two loop tracks
- Meter stick with 3 metal pointers
- Rod, stand, and two clamps
- (Optional) Plastic bins to catch runaway balls
- Fasten meter stick to rod and stand with the clamps. The bottom of the meter stick should be flush with the lowest point on the track.
- If the ball is to jump to a second track:
- For the larger ball (1.75″), separate the tips of the tracks by 14.75 inches and align them well.
- Release the ball from the very top of the track.
- The alignment is very touchy, so the jump may only be successful part of the time.
- Release the ball from one of the three heights indicated on the meter stick
- Height 1 (52.75 cm from the bottom point on the track):
- The ball will not be able to go all the way around the loop.
- Height 2 (58.5 cm)
- The ball will go around the loop and reach the end of the first track, then slide back down.
- Height 3 (62 cm)
- The ball will go around the loop and fly off the end of the track.
- Solid balls work better than hollow balls due to a smaller moment of inertia.
- If the ball is too large, it will have difficulty staying on the track.