So that means that this sound wave is a longitudinal wave, the displacement of the atoms and molecules is along the direction that the wave is moving in. So the wave is moving this way and the molecules are moving this way. Now these molecules here are going to move out that way in order to get away from the other molecules. Now here we've got the molecules very close together so that's associated with a displacement wave. So they're going to fight that, they're going to try to push apart and that means that the table is representing a medium for the propagation of a wave and that wave is going to be a sound wave. So we've got a nice little condensation of our molecules right here and they don't want to be that close together. Now down here it's not really affected but right here look what we've got, a condensation. Alright when it deforms itself, the atoms in the top layer becomes closer to each other. The acceleration will go to infinity, so what the table has to do is deform itself a little bit, now of course I've greatly exaggerated this here but you get the feel for it. So the table got to stop it, but it can't it instantaneously because that would require an infinite amount of force. Now at that point the book is moving down but the table is in the way. Now the molecules inside the table aren't really bothered until the tables comes, sorry until the book comes into the contact with the table. So here's the book falling down towards the table and what I've done is I've drawn little dots at locations of molecules inside the table alright? So there we had a loud thud right? So what happened why was there a sound wave? Well let's go ahead and look at what happened with the book as it was falling towards the table. Now what I'm going to do is I'm going to create a sound pulse and I'm going to do that by dropping this book on the table. So we need to think very carefully about how they work. And part of the reason for that is they're associated with really small displacements of lots and lots of atoms and molecules that go back and forth, back and forth many, many times per second. Let's talk about sound waves, sounds waves are actually very kind of strange things to go through and think about how they work.
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