Here's a Question! - Wet or Dry?
A dry paper towel is wadded up and crammed into the bottom of a plastic cup, where it's held in place with a little piece of tape. The cup is flipped over and lowered into a partly filled aquarium, where it's held underwater for about 30 seconds. When the cup is removed from the water, what's the state of the paper towel?
Announcer: Frostbite Theater presents... Cold Cuts! No baloney!
Joanna and Steve: Just science!
Joanna: Hi! I'm Joanna!
Steve: And I'm Steve!
Joanna: Here's a question for you...
Steve: A dry paper towel is wadded up and then crammed into the bottom of a plastic cup, where it's held in place with a little piece of tape.
Joanna: The cup is then flipped over and lowered into a partly filled aquarium, where it's held underwater for about 30 seconds.
Steve: When the cup is removed from the water, what's the state of the paper towel?
Joanna: Is it completely wet?
Steve: Is it completely dry?
Joanna: Is it just a little bit wet?
Steve: Or, is it be just a little bit dry? Which, I guess, means it's, like, mostly wet.
Joanna: Pause the video now if you'd like to think it over before we show you what happens.
Flipping the cup upside down traps air inside the cup.
Steve: For water to get in, air either has to leave, or the air has to be compressed.
Joanna: Air does leave if the cup is tipped too much. You may have noticed the water level in the cup changing when that happened.
Steve: And, the air is compressed a bit. Water pressure increases with depth, so the deeper the cup goes, the more the water gets in.
Joanna: But, for this particular arrangement, the water level remains low enough for the paper towel to stay dry. Well, as long as someone doesn't let all the air out of the cup...
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