Supplies: Small coffee can
Coffee can lid
Water

 

The Magic Can - a demonstration of pressure

The pushing force of air is called air pressure. The closer you are to Earth, the greater the air pressure. The farther away from Earth (in other words the higher your altitude), the less the air pressure. And remember, pressure is coming from all around us.

  1. Take the coffee can and punch 3 small holes in the bottom. Also punch one hold in the plastic lid.
  2. Now fill the coffee about 1/2 full of water and put the lid on.
  3. Place your hand over the hole and press down on the lid. Notice how the water streams out of the holes on the bottom due to the pressure you are exerting on the lid.
  4. Now slowly stop applying pressure to the lid. Notice how the stream of water stops. You can stop and start the flow of water simply by removing you finger from the hole. (Now would be a good time to hand the can to one of your parents...)

When you filled the can only half full, you left some space empty. This space actually was not empty - it was filled with air. Pressure on the lid exerted pressure on this air which in turn exerted pressure on the water forcing it out of the can. When you stop pressing on the lid, and leave your finger over the hole, the pressure of the air outside the can holds the water up from the bottom.

 

 

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