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

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In summary, the conversation discusses the mechanism behind a cup hissing and creating a vacuum when placed on a wet cloth. It is explained that this is a common occurrence due to the cooling and dropping in volume of hot air inside the cup. The conversation also mentions a similar experiment that can be done with a milk or juice container to demonstrate this phenomenon.
  • #1
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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  • #2
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.
 
  • #3
Awesome. Go science!

Thanks.
 
  • #4
Science rocks! Welcome to Physics Forums.

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.
 
  • #5


It is likely that the creation of a vacuum in the cup was a result of the combination of a few factors. First, the wet paper cloth may have created a seal between the cup and the surface it was resting on, preventing air from entering or escaping. Second, the warm water used for washing dishes may have caused the air inside the cup to expand and then cool rapidly, creating a lower pressure inside the cup. Finally, as the cup was tilted, the water may have shifted, causing the air pressure to equalize and the vacuum to be released with a "pop" sound. This phenomenon is known as the "hot water air lock" and is commonly observed in situations where warm water is used in a confined space. Further experiments could be conducted to confirm this theory and explore the mechanics behind it.
 

1. How did you create a vacuum in a cup while doing the dishes?

A vacuum is created when there is an absence of air. When you pour water into a cup, you are displacing the air inside the cup. As you continue to fill the cup and then flip it over, the water creates a seal, trapping the air inside and creating a vacuum.

2. Why does the vacuum only form when the cup is flipped over?

When the cup is flipped over, the water creates a seal at the opening of the cup, preventing air from entering. This allows for a vacuum to form as the air inside the cup is unable to escape.

3. How long does the vacuum last?

The length of time the vacuum lasts depends on the amount of water in the cup and the seal created. As the water evaporates or leaks out, the seal will break and the vacuum will be released.

4. Can you create a vacuum in any cup or does it have to be a specific type?

You can create a vacuum in any cup as long as it has a smooth, flat rim that the water can seal against. Cups with ridges or uneven rims may not create a seal and will not form a vacuum.

5. Is this a safe experiment to try at home?

While creating a vacuum in a cup may seem like a harmless experiment, it is important to be cautious. If the cup breaks or the vacuum is released suddenly, it could cause injury. It is best to conduct this experiment under adult supervision and use caution when handling the cup.

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