# B Cooling and its effect on particle speed

1. Oct 31, 2016

### ImpCat

Hi, I know and understand that heating a system causes the particles inside to increase in kinetic energy, due to the conservation of energy. What I don't understand is how does cooling a system causes the kinetic energy of the particles to slow down. Like how does cooling from sources such as air conditioner or ice takes the kinetic energy from the moving particles. And why would the particles give their kinetic energy away? Would be great if you can be so kind as to give me an explanation. Thanks

2. Oct 31, 2016

### ZapperZ

Staff Emeritus
I'm puzzled.

How are you able to understand "heating" ("due to conservation of energy"), but not "cooling"? Do you think that "conservation of energy" doesn't apply to the cooling process in reverse?

Maybe you should start by explaining what you have understood of the heating mechanism.

Zz.

3. Oct 31, 2016

### ImpCat

Well, in the case of heating the heat is converted into kinetic energy. That part I get. But in the case of cooling, it somehow takes away the kinetic energy? This is the part I'm confused on. Like if a system is cooled, does it mean that the kinetic energy of the particle is converted into heat, in order to keep the temperature of the system balanced or something? Like what motivates the kinetic energy of the particle to lessen? What does the kinetic energy of the particle convert to? I think I'm just confused on what "cooling" actually is.

4. Oct 31, 2016

### ZapperZ

Staff Emeritus
But you do know that "cooling" or "heating" depends on the subject in question. If I have Gas A, and I make it come in contact with Gas B at a different temperature, the temperature of Gas A will change. It will heat up, or cool down, depending on whether it was hotter or cooler than Gas B.

So while you say you understand how Gas A heats up, I can also say that at the same time, Gas B cools down! They both undergo the same process, but in reverse!

That is why I am still puzzled why you claim to understand one, but not the other.

Zz.

5. Oct 31, 2016

### ImpCat

So essentially, the process of cooling is the transfer of energy from a higher temperature gas (Gas A) to a lower temperature gas (Gas B)? Like a particle in Gas A bumps into a particle from Gas B, thus giving the Gas B particle additional kinetic energy while losing energy itself due to the collision

6. Nov 1, 2016

### jbriggs444

Yes. On average, if a faster particle collides with a slower particle, the faster will lose kinetic energy while the slower will gain kinetic energy. The reverse can happen, but the odds are against it.

Now, consider the case where a solid wall (a piston) is withdrawing slowly from a chamber with a gas that is initially at the same temperature as the piston.

7. Nov 2, 2016

### houlahound

Is it relevant to introduce laser cooling of individual atoms here?

8. Nov 2, 2016