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TheJasonKientz t1_j4xih46 wrote

Reply to comment by Fortisimo07 in What happens to the energy of sound in space? by full_hammer

The fork is vibrating. It’s never causing a pressure wave through any adjacent medium. The fork itself has energy but if it was truely in a vacuum it would never make any sound. Vibration is not the same as sound.

I wasn’t saying that the fork energy ceases to exist at the boundary of the fork, it’s just not translated into any matter as the fork oscillates back and forth through empty space. It is the atomic structure of the tuning fork itself that will cause the vibration of the fork to eventually stop. With every oscillation of the forks tines the amplitude gets a little bit smaller and the energy witching the fork translates to head which is radiated away. Or conducted away through whatever is holding the fork.

None of this is sound though. Sound is a pressure wave propagating through a medium, by definition. A tuning fork normally makes sound when there is air around it because the oscillating of the fork causes alternating low and high pressure in the adjacent air. This is the part that can’t happen in a vacuum.

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Fortisimo07 t1_j4xoykj wrote

Yeah and those "vibrations" are pressure waves traveling through a medium (the metal that the fork is made of). It's sound.

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TheJasonKientz t1_j4xseg1 wrote

It’s not a pressure wave. It’s an entirely different mechanism.

The fork tines oscillate back and forth as the metal bends at the base of the tines. There is no propagating wave through the metal. It’s really more like the motion of a spring.

Not all vibration crates sound and vibration is never sound in and of itself.

All atoms are vibrating all the time. But they are so small and there are so many of them vibrating out of sync with one another that a pressure wave never develops in any given direction.

Noise canceling headphones cancel the noise by oscillating out of phase with a sound wave so that the sound wave is canceled. So that’s a case where vibration actually eliminates sound.

Vibration is not sound.

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