Confused with mechanical waves

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Simon Bridge

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It was OK ... The x part is where it came from, the s part is where it went and the t part is how it got there.

This is not usually a useful description of sound though ... you cannot tell from looking at it where a particular bit of air came from - you only know where it is and where it is going... which may or may not mean something. But you can watch the air pressure and how it varies about some average.
 
Well usually I can translate the motion of the air molecules into pressure differences. If the air molecules oscillate a large distance (i.e. more air is compressed), the difference in pressure should be higher. Right?
 

Simon Bridge

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Difference in pressure - yes ... the maximum pressure difference would be twice the amplitude.

Excuse me it's a habit - in physics we always have to bring everything back to something that can be measured. We can sometimes physically track the displacement of air, sort of, by watching dust suspended in it. When we do that we find the actual motion of individual molecules is quite complicated even when the wave motion is simple.

It's easier to see this with water because you can see the waves on the surface (obvious up-down motion right?) and you can float small bits of neutral buoyancy stuff in it to see how the local bits of water are moving. What you find is that the actual water moves in a circle while the waves go up and down.

I think what you need to do now is look for lots of wave demonstrations online - and set up some waves yourself.
 

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