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I just saw the following video:

Floating Object

Can anyone tell me how this works? It seems to be through Bernoulli's principle, where the air pressure inside the tape roll decreases due to lower speed of the air through it. Or is it Coanda effect?

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  • $\begingroup$ Do you have a source for this video? I'm questioning if that's really feasible, or if they had some sort of string on the tape roll. $\endgroup$ – JMac Aug 30 '17 at 20:56
  • $\begingroup$ @JMac Might be.. Not claiming it to be authentic. Rather, I'd like to know whether it's feasible or not. If the air flow is strong enough, I don't see why not? $\endgroup$ – Gummy bears Aug 30 '17 at 20:59
  • $\begingroup$ I've levitated a steel ball this way, but I didn't realize that something as big as a large roll of tape could be levitated like this! $\endgroup$ – David White Aug 31 '17 at 1:43
  • $\begingroup$ Related question physics.stackexchange.com/questions/356284/… $\endgroup$ – Mauricio Jan 7 at 15:08
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Coanda. Essentially two things are going on here:

  • Coanda effect: The jet of air tend to follow the surface: so it's thrown to the right and down in this video, which (Newton's third law) means the object is pushed up and to the left; but if it goes too much to the left, it'll be pushed back by the direct "hit" of the jet. That's what makes it stable.

  • Dynamic pressure, which helps keeping the object afloat against the pull of gravity: the jet has upwards momentum, is to a great extent driven sideways as the object blocks its path and, in doing so, exerts force on it. It also keeps the cylinder next to the jet, instead of directly at it, as can happen at lower speeds.

That's very well explained in this video from the Veritasium YouTube channel: Hydrodynamic Levitation!

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