- #1
fcacciola
- 6
- 0
Hi people,
I just found out that the famous Feynman Lectures on Physics are now online, so I'm going through them just for fun (I took Physics in College a long long time ago, but was too much content with too little time to actually understand it for real, so here I'm again learning it)
In chapter 1-2, Feyman is talking about simple intuitive properties of matter as a collection of atoms, and so he let us deduce how slowly lowering a piston on a confined gas increases the gas temperature. He says
A simple mental picture and that makes sense. But then he says that "a slow expansion will decrease the temperature"
I was trying to follow that using the same ideas the let us deduce the temperature will increase if we lower the piston, i.e. compress the gas, and I noticed that I can't quite follow it from the text alone. I need to introduce a new idea: "it is the direction of the moving piston what causes the atoms to speed up or slow down. If they collide in opposite directions, the atoms speed us. If they collide in the same direction, the atom slows down".
But the problem is I just made that up. Is it correct?
And if not, then what is the "equivalently simple" explanation? The way I see it, a simple model of the collision with the moving piston *seems* to explain the increase in temperature under slow compression (since the atoms speed up), but actually falls short, as it doesn't equally explain why it decreseaes under slow expansion.
TIA
I just found out that the famous Feynman Lectures on Physics are now online, so I'm going through them just for fun (I took Physics in College a long long time ago, but was too much content with too little time to actually understand it for real, so here I'm again learning it)
In chapter 1-2, Feyman is talking about simple intuitive properties of matter as a collection of atoms, and so he let us deduce how slowly lowering a piston on a confined gas increases the gas temperature. He says
What happens when an atom hits the moving piston? Evidently it picks up speed from the collision.
A simple mental picture and that makes sense. But then he says that "a slow expansion will decrease the temperature"
I was trying to follow that using the same ideas the let us deduce the temperature will increase if we lower the piston, i.e. compress the gas, and I noticed that I can't quite follow it from the text alone. I need to introduce a new idea: "it is the direction of the moving piston what causes the atoms to speed up or slow down. If they collide in opposite directions, the atoms speed us. If they collide in the same direction, the atom slows down".
But the problem is I just made that up. Is it correct?
And if not, then what is the "equivalently simple" explanation? The way I see it, a simple model of the collision with the moving piston *seems* to explain the increase in temperature under slow compression (since the atoms speed up), but actually falls short, as it doesn't equally explain why it decreseaes under slow expansion.
TIA