This week's experiment has taken several turns. I started three different
projects, but none of them came together firmly enough to use, so they all went
back into the idea file for more work. Then, as I was washing dishes, I
noticed something fun and unusual. While washing a large water bottle, I
suddenly got a small popping sound and a squirt of water in my face.
To try this, you will need:
a large bottle with a small opening
Place the bottle in the sink. Put an inch or two of hot water into the
bottle. You don't want the water to be boiling hot. The hot water that comes
from your faucet will work fine if you let the water run until it is very hot. Once the water is in the bottle, put the palm of your hand over the opening and give the bottle a good, hard shake. Then move your hand away from the opening. You should hear a small pop, and may get squirted with some water.
Why does that happen? We would expect it if the bottle had carbonated soda, but not for plain water. Try it again with cold water. Did it work? No. The water has to be hot. Why?
When you shake the bottle, the hot water is moving through the air. That
air is heated by the hot water. When you heat air, it expands, but in this
case, the air is trapped by your hand.. That builds up pressure inside the bottle. When you move your hand, the air inside expands to equalize the
pressure. That causes it to rush out of the bottle. As we have seen in the
past, any time that air expands rapidly we hear a sound. That is why a popping balloon makes so much noise. So, as the heated air expands out of the bottle, you hear the small popping sound.
As the air rushes out, it may push some of the water out with it. That is
what got my face wet. Just be sure to clean up any mess that you make.
From Robert Krampf's Science Education Company
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