- Fill the bottle with hot water, as hot as you can handle, but not hot enough to melt it.
- Dump the hot water out of the bottle.
- Put the cap on, as quickly as possible
- Place the bottle in the middle of the table, and watch it magically crush itself.
It really never gets old.
There is a science lesson here too, of course. As the hot air trapped inside the bottle cools, the pressure inside decreases, allowing the force of the air pressure outside the bottle, to push in the sides (or something like that, it's really hard to find a clear explanation of this experiment).
But, one way or another, it's cool to watch, and when you open the bottle, it pops right back to its normal shape.
It's great to be a homeschooler.