Candy Physics - Marshmallows and Boyle's Law

I love trying to relate physics to the everyday world, it makes the concepts that you cannot see like atomic physics and electricity and magnetism easier to visualise and understand.   One of the best ways I find to do this is with food.  Either by making ice cream to discuss latent heat, using M&Ms to explain radioactive decay, or marshmallows and air pressure...

It's one of the simplest ways to demonstrate Boyle's Law, which basically states if you keep the temperature of a gas the same, the pressure of the gas multiplied by the volume it takes up will always give you a constant value. 

Or..

Initial Pressure x Initial Volume = Final Pressure x Final volume.

This demonstration is basically the TL:DR way of explaining Boyle's Law.  You increase the volume, the pressure drops and vice versa:

If you are a teacher or just want to try this yourself you can find the full instructions here