Don’t dumb it down too much
In: Physics
Sound actually doesn’t have a set speed. The general speed, 343 m/s is assuming dry air at a temp of 20 C.
So sound waves change speed depending on the density and rigidity(bulk/shear modulus) of the medium they are moving through.
It will have a different speed moving through water, or Jello, or a wall.
The speed is largely dependent on what the sound is traveling through, but this I think explains it better.
Sound is caused by a change in position of molecules relative to a collection of other molecules. Since molecules have electrons on the outside, they are repulsed from one other (like charges repulse). Thus if you change the position of certain molecules, they will repulse the neighboring molecules. These neighboring molecules will then repulse their neighboring molecules, and thus you have this “shift in position” (usually measured as a shift in pressure) that propagates through space. This is what we hear as sound. The speed of propagation depends on how close the molecules are together when they are in equilibrium, the bonds the molecules have, etc.
Also the commonly used speed of sound in air(343 metres per second ) is based on air at 20 degrees C
When you’re sending a ripple through material, there are two things that determine how fast that ripple will travel: how hard is it to move the material in the first place, and how readily does it ‘snap back’ once you’ve disturbed it. Those numbers are the density and the bulk modulus.
The speed of sound is the square root of (bulk modulus / density), and so it isn’t exactly set; the density of air changes depending on its composition and temperature, and I’m pretty sure the bulk modulus can vary but I haven’t thought about that for a long time. 😛
In solids, there’s a kind of similar calculation but it uses Young’s modulus, which I only have “oh, I’ve heard that name before” knowledge of.
Air doesn’t move large-scale when sound passes through it, the vibrations are transported by adjacent air molecules bumping into each other. This way the “motion” of the sound wave is transported very fast (about 300 m/s) without any of the molecules themselves actually moving anywhere.
**Edit:** If you’re familiar with Newton’s cradle it’s basically that concept.
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