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getting into my stride

Reged: 11/03/03
Posts: 945
Loc: lisbon at the moment
Re: Standing waves get their own thread - lucky little blighters!
16/12/04 12:04 PM
Quote Paul Woodlock:

Now for reasons I don't actually know, the maximum vibration ( anti-node )of these standing waves happens at the boundary of each surface. While the point of minimum or no vibration ( node ) occours halfway between the surfaces ( for the fundermental frequnecy at least ). this is opposite to the stnading wave in the guiter string, as the boundaries ( nut and bridge ) are always the point of no vibration. ( anyone care to exaplin this difference? .... pretty please )

There isn't really a difference, but you've got a bit confused!

Starting with the guitar string - the classic way to think about this is a load of balls (!) attached by springs. If you pluck the string the balls in the middle move up and down the most. The balls at the end move the least - obviously because they are fixed! But there's something else going on too : the springs. If you look at how the tension in the springs varies you'll see that in the middle it varies the least because two balls in the middle are at the top of the 'sine shape' where it's almost flat, so they move very little relative to each other, and hardly stretch the spring at all.

On the other hand if you look at the springs right at the end you'll see that the tension varies the most because one ball is fixed and the next moves up and down in the steep part of the 'sine shape'.

So, going back to air - the movement of the air right next to the wall is zero just like the guitar string. But the pressure variation right next to the wall is maximum which is why you can hear the bass there (your ears are measuring the pressure variation, not the air movement).

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