Can Crush (Demo)

Vacuums suck!

 

 

 

Category - Solids, Liquids & Gases

Key Idea - Air Pressure

 

Purpose - I have used this to show the effects of a vacuum and also when teaching the properties of liquids vs. gases 

Apparatus set up ready to crush a can.

 

The end result!!
Nature -  Demonstration
Materials -  Some kind of metal container with a screw on lid (unused petrol tin is perfect, but expensive), Bunsen burner, tripod, access to water
Method - 
  1. Put about 3 cm of water in the bottom of the tin.
  2. Put the tin on the tripod to heat (with the lid off)
  3. Once the water is boiling vigorously, turn off the heat and seal the tin with the screw on lid.
  4. Go on teaching until you hear the distinctive tinging noise that indicates immanent implosion, and watch the fun!
  5. A faster variation is to run cool water over the tin as soon as it is sealed. The tin should crush within a few seconds this way. 
Safety - The usual precautions with heat. Sometimes the crushing can will move violently, so a bit of distance around the tin is recommended. If you use a tin that has previously held flammable liquid it should be thoroughly rinsed before use.
Explanation - As the water boils the vapor fills the tin, forcing air out to make room. Once the water vapor starts to cool and condense back to a liquid it takes up less space, but the air cannot move back into the now sealed tin to replace it, so a partial vacuum is created. Atmospheric pressure forces the tin to implode. 
Notes - This demo is a fantastic attention getter that always impresses. You can usually obtain free cans that were used for cooking oil from your local snack food or fish & chip shop, although the oily residue inside can be yucky to clean out.   

This demo can be used as a preview for the Can Crush Practical to good effect.