What makes popcorn pop?

I have to say a big THANKS to all the parents who are turning in Box Tops and clipping them so nicely. It really makes counting go by fast when they are nice and trimmed.
This week we're having a popcorn party for Kindergarten who turned in the most Box Tops in November (yes, we're a little behind on this but catching up fast!). The timing couldn't be better because they are studying why popcorn pops. PTO is bringing out the popcorn cart so they can see and hear it in action. I've never used the cart before and I'm hoping it's easy to use so that we can wheel it out at other PTO events.

So just how does popcorn pop? Here's the answer from the NASA for kids website:
http://www.nasa.gov/audience/forstudents/index.html
Only popcorn kernels can pop, and the secret is water. Each kernel contains a small amount of water stored in a circle of soft starch inside the hard outer casing. When heated to around 450 F, the moisture turns to steam, creating pressure within. As the pressure builds, the casing eventually gives way, and the kernel explodes and pops, allowing the water to escape as steam and turning the kernel inside out. If you have ever popped popcorn, you know that it explodes everywhere!