Shrinkies

OK, so you can't really shrink people like they show in movies. But here's a fun experiment you can do with something that actually does shrink.

What you'll need:
Foam plastic plates
Scissors
Markers
Foil
Oven set to 350^o
Oven mitts

Cut out small round or rectangular pieces from the flat bottom of the foam plates. Draw pictures on them with the markers. Arrange them on a piece of foil so that they are not touching, and heat in the oven for 4-5 minutes, or until they have shrunk. Take the foil out of the oven carefully using the oven mitts and let the shrinkies cool. You will see a miniaturized version of what you originally drew!

So, why does this kind of shrinking work? The foam has a Swiss-cheese-like structure, with lots of air holes. When you heat the piece of foam, the air bubbles collapse, and you end up with a solid piece of plastic. You have actually changed the density of the plastic, by decreasing the volume, keeping the mass (weight) the same.