Challenge your students to predict what will happen when you let go Materials Bunch of keys Keyring Shoelace Pencil or pen Instructions Tie your keys to one end of the shoelace and a sing ID: 427836
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© Ruben Meerman 2004 Teacher Demonstrations Challenge your students to predict what will happen when you let go Materials: Bunch of keys / Key-ring / Shoelace / Pencil or pen Instructions: Tie your keys to one end of the shoelace and a single key-ring or ring. A single granny knot is sufficient to tie them. You can do this in front of the class anticipation can be the best part of a demonstration. Hold the single key-ring and let the bunch of keys hang over the pencil as illustrated. Ask if anyone would like to predict what will happen when you let go of the key-ring. If no-one re Let go of the key-ring. The ring times causing the keys to remain hanging from the pencil. Explanation: This is could be thought of as a pendulum trick. A pendulum usually swings to the height from which it is length of the shoelace hanging over the pencil on the key-ring side gets shorter. By e pencil, it is being lifted up by the heavier weight of the keys falling on the other end. The key-ring ends up with much more kinetic energy than is required to reach the height from which it was released so it overshoots and wraps around the pencil. Friction takes over once the shoelace has wrapped around the string a few times and stops the keys falling any further. See also: Science Conundrums Pendulum Problem