Balloon Scale
		Materials: Two balloons A yardstick Some string A sharp object

Procedure: Inflate the two balloons and tie them closed, then use the string to hang them from opposite ends of the yardstick. balance the yardstick on your finger. Now pop one of the balloons.

Explanation: The yardstick becomes unbalanced as the popped balloon loses the mass of air it held. The two rubber balloons still weigh the same, but the inflated one now holds more air, which makes that end of the scale heavier, so it sinks.