I just created a vacuum in a cup when doing the dishes?

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riskybeats
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I want to know the mechanism behind this. I folded a paper cloth (may of been of the bounty kind), and put my wet cups on there mouth down. I heard a hissing, and I thought I may have left the stove on. I followed the noise to the cup, and noticed it was hissing like crazy. I tilted the cups mouth off of the cloth, and met quite a bit of resistance. When I got it off, it made the 'pop' noise of a vacuum being destroyed.

Any theories on how this happened?
 
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The hot cup had hot air in it. As the cup cooled the air inside cooled and dropped in volume. This is a common occurrence.
 
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You can do a similar experiment with a milk or juice container. Put about 1/2" or so of cold tapwater in the container, cap it, and shake it. The shaking helps the water cool the inside air quickly. This will create a slight vacuum, and a rectangular milk carton will be noticeably deformed.

Next, dump the water and put in 1/2" or so of hot tapwater, cap, and shake. That will heat the air, creating higher pressure in the carton.