What are causing the cup to fly out?

  • Context: High School 
  • Thread starter Thread starter moment1337
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Discussion Overview

The discussion revolves around understanding the forces at play when one cup flies out of another during an experiment involving blowing air between them. Participants explore the underlying physics, including concepts of air pressure and force interactions.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant notes that blowing air between the cups seems to create a force that pushes the top cup up and out.
  • Another participant proposes that air pressure builds at the bottom of the outer cup, pushing the inner cup upward, but their experiments did not confirm this hypothesis.
  • A later reply questions the effectiveness of cutting holes in the bottom of the outer cup, suggesting that air may still flow in a way that allows the top cup to pop up.

Areas of Agreement / Disagreement

Participants express similar hypotheses regarding air pressure and force, but there is no consensus on the exact mechanics or outcomes of their experiments. Multiple competing views remain regarding the effectiveness of modifications to the cups.

Contextual Notes

Limitations include the lack of clarity on the specific air flow dynamics and the effects of different modifications to the cups. The discussion does not resolve the underlying physics or confirm the validity of the proposed explanations.

moment1337
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Hello. I need some help of understanding what forces are causing one of the cups to fly out of the other one when you blow at it. This video describes the experiment.
 
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Mo,
It looks as if the individual is blowing right between a cup and the one just above it.
When you blow, what are you doing to the air?
As a hint, if the air is blown between the top cup and the one underneath, it must be the air creating some kind of force to push the cup up and out.
Can you maybe try to give a some kind of explanation on your own now.

PS. You might understand it better by thinking about it some more, than just reading an explanation.
 
I have been doing quite a lot of tests on my own now and has sort of came to the conclusion that air pressure is forming at the bottom of the outher cup and pushes the inner one up. I tried verfiying this by cutting out of the bottom of the outer cup, thinking that this would cause the air to escape underneath. Unfortunately this did not happen to be the case.
 
I would have come to the the same conclusion.

By cutting out the bottom of the outer cup, did not the air flow out the bottom or was it not able to.
Tried it myself with poking holes in the bottom of paper cups, and the top cup still wants to pop up.
 

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