A few months back, I offered up an experiment that showed how cold affects the density of water. Now, as a companion piece, I suggest this Demo Science science demo on the similar effects of heat on air. Like The Godfather Part II, The Empire Strikes Back, and Weekend at Bernie’s 2, I think the sequel betters the original.
Let’s Blow This Pop
This one requires a bare minimum of supplies. All you need is an empty plastic soda bottle, and the cap for said bottle. I guess you need hands, too, but that’s kind of a given. If you don’t have hands, this experiment will be considerably more difficult, though not impossible.
First, wet the cap of the bottle. I recommend using water (oh yeah—you also need water for this demo), but literally any liquid will work. I can think of a few liquids I would absolutely not use, but ultimately it’s up to you.
Place the cap upside down on the top of the empty bottle. Then, wrap your hands lightly around the bottle. Hold it firmly, but gently. Don’t squeeze it, because that would be cheating the science, and if there’s one hard and fast rule I live by around here, it’s “never cheat the science.” I realize that’s the first time that’s ever come up, but I swear that phrase has been the guiding principle of this blog since Day One. Never. Cheat. The science.
Ask your students (or whoever you’re doing this experiment with) what they think will happen. It might take a while for the desired result to happen, so the smelly little buggers should have plenty of time to speculate.
After a hot minute or two, the cap will “jump” off the top of the bottle of its own accord. What the come on now won’t ya hey just happened?
Science Happened, Man!
When you wrapped your beefy mitts around the bottle, they gradually warmed the air inside the bottle. As the air warmed, its molecules expanded and, at a sub-microscopic level, those molecules began to vibrate at a faster rate as they fought to expand and escape the confines of the bottle.
The wet cap sealed the bottle just enough to keep the air inside. A dry cap would not have this effect—the miniscule amount of water on it created a weak but complete seal around the opening. However, as the air got warmer and warmer, and its molecules expanded more and more, it pressed against the cap hard enough to break the seal. With the cap out of the way, the air escaped the bottle and, as it moved into open space, without your sweaty meat hooks around it, cooled back to its original temperature.
A good follow up to your first run-through is to let some (or all) of your students get in on the action themselves. Re-wet and reposition the cap, and let someone other than Kevin have a turn. What do the kids think will happen now? The same result? Will it take longer because kids’ hands are smaller? Will it go faster because kids are dumb and will probably ignore the instructions and just squeeze the sides of the bottle? The only way to definitively answer these questions is through some good old fashioned sciencing, so have at it!