The Collapsing Can

Equipment

Water, 1-5 gallon can fitted with a rubber stopper or valve, ringstand, large iron ring or large clamp, Bunsen burner and gloves for handling hot can.
Alternatively: Aluminum soda can, tongs, and a 2-liter beaker filled with ice water, wire screen for the burner or hotplate.

Presentation

1. Add water to the can to a depth of approximately 1 cm.
2. Heat the water in the can until steam issues continually from the can. Caution, the burner flame can quickly burn a hole in the aluminum can. For a 5 gallon can, the steam should be allowed to issue for a minimum of 5 minutes.
3. Turn off the Bunsen burner and quickly stopper the can or close the valve. OR Remove the aluminum can from the heat with the tongs and quickly invert it in the beaker of ice water.
4. You may speed the cooling of the gallon cans by spraying them with cold water.

Hazards

The hot can, water and especially the steam can cause severe burns.

Discussion

The boiling water displaces air leaving the interior of the can filled almost entirely with water vapor at atmospheric pressure. As the can cools, the interior pressure equals the vapor pressure of water at that temperature. At 25° C the vapor pressure of water is approximately 20 mm Hg, the pressure differential is approximately 14 lbs/in² or for a rectangular can whose dimensions are 4" x 10" x 8" the total pressure exerted on the surface of the can is:

[2 x ( 4 x 10 ) + 2 x ( 4 x 8 ) + 2 x ( 8 x 10 )] x 14 = 4.2 x 10³ lbs

or approximately 2 tons.

References

1. Alyea and Dutton, p. 23(10-1).