COLLAPSING CANS AND BARRELS :  DEMONSTRATE THE "POWER OF PRESSURE"

The story goes that Scott Kittelman (or the class TA) took a barrel full of (see below) up Mt. Evans for a party.  They drank it all and then closed up the barrel and drove down the mountain.  The barrel collapsed because of the increase in air pressure acting on a container with a large surface area.

Physics Lab may have a big one lying around.

Ours is a little one (how could the part crowd finish off the big one (55 gallons) in one sitting):

A MORE ACTIVE DEMONSTRATION:

1. An alternative demonstration is to invert a pop can that has been heated into a water bath.
2. Fill the glass dish with about 1/2 inch of cold water.
3. The can should first be laced with a little water (a few tablespoons full) inside.
4.  Hold the can in tongs.  It is then heated with the torch until steam come out. Move the torch around, don't burn a hole through it.
5. Grab the can with the glove and invert it.  Seal it to the rubber base in the basin.
6. The can should collapse.

Questions:

1. What is the role of the water in the can?
2. Does it work with no water (try it), relying on PV= RT inside alone?

©2000.  John Hart, University of Colorado