Faith in the conservation of energy is tested by taking the demonstrator's nose to task.
What it shows:
The principle of conservation of energy ensures that a pendulum released at a particular amplitude will not exceed that amplitude on the return swing. A lecturer's faith in their subject is put to the test using a 50lb (22.7kg) iron ball.
How it works:
Technique is very important here. The best method to employ is to stand with your back against the blackboard with your head also touching the board. This ensures that you don't lean forward after release. Pull the ball towards you, holding it on the far side from your face (your hands between it and your face may result in you giving the ball a little push...). Release by sliding your hands aside.
Setting it up:
Galileo's Chandelier describes the setup of the cable for the Skyhook pendulum. The iron ball clips onto this cable in the same way as the bowling ball.
Although the iron ball is suitably massive, the bowling ball could also be used - the audience KNOWS a bowling ball is not the sort of thing you want on a collision course with your nose; the iron ball could be any weight. Keep your eyes open - you'll get more of a kick out of this than the audience!