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Floating Bag

Material List:

  1. yardstick
  2. block of wood
  3. 2 medium sized paper grocery bags
  4. needle
  5. string
  6. scissors
  7. Incandescent lamp

Drawing of floating bag


Open the grocery bags and poke a hole in the center of each bag's bottom. Cut two strings of equal length and tie a knot at one end of each string. Insert the strings through the holes in the bags and tie the loose end exactly 1" from each end of the yardstick. Set the block of wood on the corner of a desk so the yardstick will move freely without obstructions. Be careful to make sure the yardstick is perfectly balanced. Place the incandescent lamp under one of the grocery bags and turn it on. Watch what happens.

Scientific Principle:

The incandescent bulb will produce heat. The warmer air stream will replace the colder air that is in the bag. As the colder air is replaced with the warmer air, the bag becomes lighter and will rise. This demonstrates that warm air is less dense than cold air, and that cold air of equal volume will weigh less than warm air. Since cold air is heavier than warm air, cold air will fall pushing the warmer air up.

Related Pages:
Convection Home Page
Aeronautics Activities
Aerospace Activities Page
Air Density
Aerodynamics Index


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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: May 13 2021

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