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Square Ring of Air?

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Watch the video on YouTube.

What kind of experiment is this?

Experimental procedure and explanation:

  • What if we try the “Ring of Air” experiment using a square hole?
  • If you try it, you can see that it still creates a round ring.
  • With a square hole, the water inside will come out in a square-pole shape, forming a core. Viscous friction will act between this core and the stationary water around it, initially forming a square vortex ring.
  • However, this square vortex ring will quickly change its shape to a stable, round vortex ring. Therefore, the subsequently formed air ring becomes round most of the time. We can see that a round ring is created regardless of the shape of the hole.
  • From this, you can tell that the air does not have to be blown in a continuous, round shape; it could have fine bubbles around it, or you can spurt water with appropriate amounts of air mixed into it. The hole through which the water passes does not have to be round.
  • The way to make a good vortex ring is to spurt out water vigorously over a short duration and to have bubbles as fine as possible. The faster the rotation of the vortex ring, the more air gets collected.
[Related items] Air Cannon, Ring of Air, Centrifuge
[Reference] “The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs pp. 52–59.
Last update: 1.21.2015