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This is a simple demonstration experiment that can be used to show the effect of air pressure by using it to crush a metal can. It addresses some fundamental properties of air pressure in an easy to explain attention grabbing fashion.

List of equipment needed:

Unvented empty 1 gallon metal can with spout:
Typically duplicator fluid can or varnish can, a new gasoline can could be used if the appropriate spout could be found and pop vent can be hold seal.

A six to ten foot length of rubber tubing.

a clamp for the rubber tubing

cloth tape

A bucket or tub with a capacity of more than a gallon.

A stable large desk or table top on which a demonstrator can stand safely.

The gallon can is filled to capacity with water then the top with spout screwed into place. Then the rubber tubing is place over the spout and taped to seal connection airtight. The opposite end of the tubing is placed in the bucket which is near the desk.

At this point the clamp is placed on the tubing and the demostrator is instructed to go to the desk where he/she is given the can and told to hold it with the spout pointing down and at least head high. The clamp is then released and the water is allowed to run out of the can and into the bucket.

With all seals maintained airtight, as the water leaves the can it begins to collapse or seemingly be "crushed". When this happens you can usually start to ask the astounded demonstrator; "What are you doing to my can?" or other such questions.

The advantage of using a gasoline can for this demonstration is that by opening the can's vent air can be easily reintroduced and the can recover.

The reason for the "crushing" of the can is the push of the ocean of air that surrounds us. The length of tubing and the elevation of the can are used to overcome air pressures ability to block the flow of liquid from an inverted container. Once the water is removed from the can there is nothing (that means absolutely nothing) inside the can to keep the air from crushing the it. At sea level the pressure is about 15 pounds per square inch on every side of the can. With the water gone the wide side of the can, which is about 50 to 60 square inches in area has about 750 to 900 pounds pushing on it!

This demonstration shows that air is "something" and it points out how a difference in pressure effects things.