Scavenger Hack: Demonstrate center of mass with forks and toothpicks

This is a fun bar trick. You can balance two forks and a toothpick on the tip of another toothpick. The above picture shows where I take advantage of a salt shaker for a base. But there are many variations of this trick as seen in the following videos.

The way this works, is the two forks lean downward putting more than half the mass below the toothpick balance point. Falling requires moving the center of mass lower. Since more mass is below the balance point already, most movement actually raises the center of mass.

This creates a stable situation where falling can’t easily happen. Any disturbance upward ends up falling back to this stable position. This is an example of negative feedback.

If you were to just try and stand a fork on end, then you would have an unstable situation. If the fork were to lean slightly, or get a slight disturbance, the center of gravity would get a bit lower. As the fork falls, the center of gravity gets lower still. The falling speeds up. This is an example of positive feedback.

You can go to arvindguptatoys for step by step photo instructions, or watch these videos:

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