Hyperloop: riding sound’s density peak to exploit the drag equation?

Re:Hyperloop: riding sound’s density peak to exploit the dra... by throwmeaway33 on Thursday July 18, 2013 @05:06AM (#6062563)

I remember doing the math in my undergraduate physics studies. Air molecules actually do not move very far when a vibration (ie. sounds) goes through them. Amazingly, high frequency sounds move air back and forth only a few angstroms.

I can't find a link describing the calculation. This link talks about how the change in pressure is equivalent to "140 molecules for every million molecules" http://www.silcom.com/~aludwig/musicand.htm

So there is no way you are going to create a bubble of vacuum!

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Re:Hyperloop: riding sound’s density peak to exploit the dra... by geon on Thursday July 18, 2013 @05:41AM (#6062638)

The article talks about low frequency and high amplitude. The sound waves near a subwoofer definitely moves the air more than a few ångström...

And you don't want low pressure, but high, so the air speed is low. Drag is proportional to the density, but proportional to the square of the speed.

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Re:Hyperloop: riding sound’s density peak to exploit the dra... by cma on Thursday July 18, 2013 @05:12AM (#6062573)

Not trying to create a bubble of vacuum (though that was my old idea =).. then I realized what you lost gained by low density you paid for in high velocity).

Also, the idea here isn't involving high frequency sound.

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Re:Hyperloop: riding sound’s density peak to exploit the dra... by hotpockets on Thursday July 18, 2013 @11:07AM (#6064112)

In the long wavelength regime, frequency is proportional to 1/wavelength. In fact, frequency=speed/wavelength.

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