Video: Watch this demo
Professor Walter Lewin doing the demonstration
Description: This demonstration illustrates the conservation of energy of a pendulum.
The potential energy of the pendulum gets converted into kinetic energy and then back into potential energy
when it reaches a maximum height at the other side. The pendulum won’t hit your face because it does not gain energy.
Equipment:
- Long rope
- Two S-hooks
- 10kg weight
- ladder
Setup Procedure:
- NOTE: This demo can ONLY be done in rooms 20, 124, 126, 134 or another room in which the ceiling can safely support a VERY LARGE amount of weight.
- NOTE: If you tie a Taut-line hitch in the rope, you can easily and quickly adjust the height while not worrying about the knot slipping!
- Using the step ladder, hang the 10kg mass from the ceiling using the S-hook.
- Standing against the door (where the professor or demonstrator will be), pull the pendulum up to your chin to make sure that the rope is the appropriate length.
- If the rope is too long or too short, move the hook along the bar, or adjust the length of the rope accordingly.
- Also make sure that when let go, the pendulum will NOT HIT any students or equipment in the lecture hall!
Demonstration Procedure:
- Stand with your back and head against the wall (to make sure that you don’t move forward and hurt yourself, and to prove to the class that you can’t move backward and out of the way) and pull the pendulum up to your chin.
- Let go of the pendulum (but DON’T give it any push!).
- Don’t worry: it can’t hit your face, as long as you don’t move!
Concepts: Conservation of energy is demonstrated.
22-C3
