Inertia - Small Steel Ball
To demonstrate inertia of rest.
Stand with spring, card, and ball, as photographed.
This experiment is useful only for small groups.
A spring is pulled back and released, flipping the card away so that the steel ball falls into the cup. A small flat has been filed onto the ball so that it will rest in position on the card.
Haym Kruglak and Robert Scherzer, An Applause-Winning Inertia Trick, TPT 33, 284 (1995).