I enjoy cooking, but I’m pretty lazy about it. Therefore, I make pasta a lot. One of my favorite things about cooking pasta is the “pasta schvitz” as I call it—holding my face in the steam coming off the pasta when I strain it from the boiling water in which it was cooked. It’s like a miniature, temporary sauna, and it makes my ol’ mug feel pretty great afterwards.
Yes, steam can do some pretty amazing things. This Demo Science science demo, while it does not involve the preparation of delicious pasta, will give your students an interesting example of how steam (and condensation) work. Speaking of cooking…
The key piece of equipment for this experiment is a microwave, so you’ll either have to bring one into the classroom yourself like some kind of weirdo, or take the whole class down to the kitchen. Ask the lunchlady or lunchladies ahead of time, of course—lunchladies don’t take kindly to unannounced visitors, and you don’t want to see how the sausage is made, trust me.
You’ll also need at least one small to smallish balloon (but bring several just in case) and a thin-walled plastic receptacle. An empty 20-ounce or 2-liter soda bottle will work fine, but if you really want to “wow” the lunchladies whilst you’re down their way—and who doesn’t, amirite?—get a custom-made bottle. (I got a guy who does PEEK machining and can whip you up something real fancy-like, if you’re interested.) You’ll also need a little bit of water, but how much is tricky to say definitively—results may vary, so you may want to run this demo at home once or thrice before you show your students, just to get a gauge on the optimum amount of water.
Put the ideal amount of water into the bottle, probably around a tablespoon or so. Then, pop the bottle in the microwave and turn the microwave on. Nuke it until the water is boiling, then let it go a little longer until the water is almost entirely boiled away. Using a towel or oven mitt (you’ll also need a towel or oven mitt for this demonstration) take the bottle out of the microwave and set it on the counter. Quick as you can, slip the mouth of the balloon over the opening of the bottle. Then stand back and watch the magic science.
Prepare for Keanuing
If all goes well, you’ll probably hear a number of “Whoa”s. As the small volume of boiling water became steam, it increased in volume in its gaseous form and filled the whole bottle. When you stopped the microwave and removed the bottle from the heat, the steam immediately started to cool and would slowly have condensed back into water, all the while gently pushing warm air out the bottle’s spout—had you not stuck the balloon on top.
Instead, the escaping warm air filled the balloon (at least partially). Then, if you got just the right amount of water, the balloon got pulled into the bottle. This happens because, as the air cooled, and the air in the bottle below cooled and the water condensed, it contracted. At the end, your bottle will have the same amount of water in the bottom that you started with.