Dynamics Activity
Coins and Hoop

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Purpose:

Demonstrates "objects at rest tend to stay at rest"

Equipment:

stack of coins

embroidery hoop

small flask

Description:

Balance the embroidery hoop on the flask, then balance the stack of coins on top of the hoop. Challenge: Put the coins in the flask without touching them.

Explanation:

Hint: Quickly grab the far side of the embroidery hoop and jerk it out from under the coins. This will momentarily stretch the hoop horizontally, breaking contact with the stack of coins without disturbing it. The coins then fall into the flask (Newton's First Law).

If you grab the near side of the hoop first, you momentarily stretch the hoop vertically, so that the coins are tossed into the air - they may or may not land in the flask.

adapted from Robinson, Conceptual Physics Laboratory Manual, Addison-Wesley

last update January 6, 1997 by JL Stanbrough (Questions, comments, and suggestions are welcome at jerry_stanbrough@bhs.batesville.k12.in.us)