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enter image description here These are the upper and lower discs A and B. There is a small hole in the center of A, and a pipe is connected to the small hole. The pipe is connected to compressed air. We use B to approach A. When the distance between A and B is far enough, A and B are repulsive forces. However, when A and B are close enough, A and B are attractive forces. Attractive force can even be greater than the gravity to which B is subjected. Why is that?

This video shows this.

enbin
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  • https://www.exploratorium.edu/snacks/bernoulli-levitator – sammy gerbil Nov 23 '17 at 13:03
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    -1 Not clear what you are asking. Why do you say that this phenomenon does not appear to be explained by Bernoulli's law? – sammy gerbil Nov 23 '17 at 13:14
  • @sammy gerbil I think it's because of air inflation, so it's not Bernoulli's law that explains it. – enbin Nov 23 '17 at 13:51
  • Ah I see that you uploaded both videos. I do not understand your explanation. What do you mean by air inflation? How is this different from Bernoulli's principle (increase in air speed causes reduction in pressure)? If air inflation/expansion is correct then the lift force should be strongest when the gap is wide. Instead the lift is strongest when the gap is narrow, as Bernoulli's law predicts. – sammy gerbil Nov 23 '17 at 16:19
  • @sammy gerbil Bernoulli's law can not be applied to the condition of air expansion, but in fact the air on the upper part of the wing expands and produces lift. I added some content to the question to explain what I mean. – enbin Nov 24 '17 at 12:20
  • Possible duplicate of What really allows airplanes to fly? – Kyle Kanos Nov 24 '17 at 14:19
  • Now you are asking about two different situations : the paper plate and the airplane wing. You are also bringing in viscosity, which does not appear in Bernoulli's equation. You are not making your question clearer, you are making it more confusing! ... Your additional question about airplane wings has already been asked (and answered) many times on this site. Your original question about the paper plate does not appear to have been asked before, so I think you should remove the question about the wing and stick to the paper plate. – sammy gerbil Nov 24 '17 at 18:18
  • It's not Bernoulli. It's not how wings work. It's the Coandă effect, the tendency of flows to attach to surfaces. – Mike Dunlavey Nov 25 '17 at 01:41
  • @sammygerbil I see your explanation, but your explanation is wrong. B is absorbed because the air expands, so the pressure decreases. Bernoulli's law is not used in air expanding fluids. Bernoulli's law can only be used in incompressible fluids. The gas ejected from the nozzle is moving, but its pressure does not decrease as a result. – enbin Mar 20 '19 at 14:22
  • @MikeDunlavey Why do you think it is the Kangda effect? – enbin Feb 18 '20 at 16:37
  • Possible duplicate by OP: https://physics.stackexchange.com/q/471093/2451 – Qmechanic Oct 04 '20 at 04:48

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