Fluid Mechanics

Double Bubble

What it shows

When two different size soap bubbles are connected together, the smaller diameter bubble will shrink and collapse to blow up the larger diameter bubble. One can use this to demonstrate Laplace's law or the phenomenon of minimizing the surface area of a soap film.

How it works

Laplace's law tells us that the gauge pressure of a spherical membrane is given by 2γ/r, where γ is the surface tension and r is the radius of the sphere.1 For soap bubbles (which have an inside as well as outside surface), the gauge pressure is twice...

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Fakir Physics

The concept of pressure is demonstrated by lying on a bed of nails.

What it shows:

The lecturer (or someone else) lies on a bed-of-nails without discomfort, thus demonstrating the concept of pressure, which is the force per unit area. For added drama the person is sandwiched between two beds of nails with the added weight of a cinder block on top. The cinder block can be broken with a sledge hammer.

figure 1: A supermarket tabloid reports on how macho man pulls off this stunt.

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Vacuum Cannon

If you're feeling pressure to do something fun, consider the vacuum cannon...

See slow-motion footage of the Vacuum Cannon in action (https://youtu.be/gex5Fq5oUtc)

What it Shows

Air rushing into an evacuated tube pushes a ping-...

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