In this clip you can actually "see" a sonic boom. As the jet approaches the speed of sound it catches up with the roar of its own engines, packing sound waves tightly together. In the humid sea air, the pressure on the leading edge of these waves causes water to form tiny droplets, revealing to our eyes the wall of air against which the plane is pushing. Breaking through this wall is in fact breaking the sound barrier. For more pictures of sonic booms, check out: SkyFlash.

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The Rubin's Tube acts as a physical visualizer, exploiting sound's compression of air to vary the flow of gas to a set of flames. What we're seeing is the result of standing waves set up inside the tube. You can see the wavelengths of the waves produced in the tube as the frequency (pitch) is changed. So tell me; can you work out the frequencey of the unnamed tones by counting the waves?

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Just as the Rubin's tube set up a standing wave in air, here we have a standing wave in glass. You can see the glass vibrate in and out. The points where it doesn't seem to move are the nodes of the standing wave, like the low points of flame above. Eventually it's too much for the glass, and we get the spectacular end we hoped for. This is a classic example of resonance.

This clip is from the Department of Astronomy and Physics at USC. Check out some of their toys.

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It might have been a Beach Boy's video, sand tousled about atop a vibrating plate. Again, it's resonance at work, the sand settling into the relatively calm nodes while the plate vibrates. Unlike the wine glass, here we see our subject vibrating at multiple harmonics as the frequency of vibration is varied. This brings about the many different patterns we see.

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Just as we saw resonance in the Rubin's Tube and wine glass, here we see the resonance of air in a box. We are aided in this by the presence of bits of what appear to be polystyrene riding on the pressure wave in much the same way as we saw water condense during the sonic boom. This is actually very similar to our Rubin's tube and is an example of Helmholtz resonance.

This video was provided by Dr. David Deak who maintains the website Deak World.

LINKS GOOD ON 2006-12-14