Atmospheric Mass

This activity will demonstrate that the air in our atmosphere has mass which is attracted by the force of gravity.

Time requirement: 40 minutes as an activity, 15 minutes as a demonstration.

Materials

Procedures

  1. Inflate the two balloons to approximately the same size. Tie the ends of the balloons so that the air does not escape.
  2. Using the string, suspend the balloons from opposite ends of the dowel.
  3. With another piece of string attached near the middle of the dowel, balance the dowel and the two balloons. A piece of tape at the balance point will help prevent the string from slipping.
  4. When the dowel and balloons are balanced, suspend the apparatus from some fixed point so that you are free to continue.
  5. Place a drop of oil on the outside of one of the balloons.
  6. Insert a pin through the oil into the balloon. The balloon should not explode.
  7. Allow the balloon to deflate. The escaping air may cause the apparatus to swing around.

Observation questions

  1. Describe what happened to the balanced dowel and balloons when one of the balloons was deflated.
  2. Why did the dowel become unbalanced when all of the air in one of the balloons escaped?

Last updated: March 17, 1998
Joe Twicken / joe@nova.stanford.edu
Rob Wigand