Popcorn Physics with my Pre-schoolers

As we were eating our bed time snack this evening, I started asking my kids about why popcorn pops.  My son said, " I don't know."  He was interested though (kids are always interested in science!), so I explained that the kernels had water inside of them.  I asked whether the energy was going in or coming out of the popcorn.  (It's going in.)  I explained that the energy going in changed the water from a liquid to a gas.  We examined a popped kernel to see where the seed coat ended up.

Then my son had a better idea.  

He said, "I wonder what happens when you put popcorn in water."  I retrieved a dish of water, and we dropped popcorn into it.  We dropped in popped kernels.  Did you know popped corn fizzles when it is dropped in water?  We dropped in the un-popped kernels.  They floated just liked the popped kernels.  That got me thinking.  What about un-cooked kernels?  They sank!   Eventually the popped kernels began to sink as well, but the cooked, un-popped kernels continued to float.  

So, as I had been saying, the water leaves the kernels when you cook them.  Apparently sometimes the water boils out of the kernel without bursting the seed, but water does not penetrate the seed coat as easily as the popped corn.  The uncooked popcorn is more dense (particles packed closely together) than either popped or un-popped kernels that have been cooked, which is why it sinks when they float.

My husband noted that the buoyant principle is important in this phenomena as well.  The greater volume of water the popcorn displaces, the more force the water exerts up on the piece of popcorn.

What else is important about popcorn?