In the diagram below, A is a disk and C is a pipe, the A and C combination is a nozzle, B is a board. As long as B is close enough to A, with the air from the D, B will be sucked and will not fall down. Why is this the case?

I don't think this phenomenon can be explained by Bernoulli's law, because the air in the gap expands. Because the air moves outward, the radius of the nozzle is larger, and the volume of the gap between the A and the B passing through the air is proportional to the square of the radius. Low pressure due to expansion. B doesn't fall because of low pressure. This video shows this.

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    $\begingroup$ youtu.be/eR1SD00NtEU $\endgroup$ – enbin zheng Nov 23 '17 at 11:54
  • $\begingroup$ exploratorium.edu/snacks/bernoulli-levitator $\endgroup$ – sammy gerbil Nov 23 '17 at 13:03
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    $\begingroup$ -1 Not clear what you are asking. Why do you say that this phenomenon does not appear to be explained by Bernoulli's law? $\endgroup$ – sammy gerbil Nov 23 '17 at 13:14
  • $\begingroup$ @sammy gerbil I think it's because of air inflation, so it's not Bernoulli's law that explains it. $\endgroup$ – enbin zheng Nov 23 '17 at 13:51
  • $\begingroup$ 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. $\endgroup$ – sammy gerbil Nov 23 '17 at 16:19

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