A medium large spoon, like one used to serve peas, with a bowl 2.5 cm or more wide.

Assembly

Bend the handle back over the top of the bowl of the spoon, but not over the center of the bowl. Bend it off to one side so that it passes through a point about 1/2 way between the center of the spoon and one edge of the spoon.

To Do and Notice

Put the spoon on a table top so that it rocks back and forth nicely.

Tap the end of the handle down.

The spoon starts rocking, then the rocking turns into rotation. Notice the direction of the rotation.

When the spoon stops, spin it opposite this direction. It will stop rotating, vibrate a little and then rotate the other way.

What's Going On?

Although it seems at first like the spoon violates conservation of angular momentum, it doesn't. The table exerts torques on the asymmetrically weighted spoon that make it rotate.

Reference

Thanks to Claes Borjesson of Tom Tits Experiment for showing me this activity.

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Scientific Explorations with Paul Doherty

© 2000

1 Feb 2000