Tornado in a Bubble

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In this video, a miniature tornado-like vortex is created inside a soap bubble.  Here’s how it works: after the first bubble is formed and the smoke-filled bubble is attached to the outside, he blows into the main bubble, creating a weak angular velocity, before breaking the interface between the two bubbles.  As the smoke mixes in the main bubble, note how it is already spinning slowly due to the free vortex he created. Then, when the top of the bubble is popped, surface tension pulls the bubble’s surface inward. Because the bubble radius is decreasing, conservation of angular momentum causes the angular velocity of the fluid inside to increase, pulling the smoke into a tight vortex, much like a spinning ice skater who pulls her arms inward.

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