# How to simulate pressure in an ideal gas simulation

1. Oct 15, 2012

### leibo

Hello

I wrote a simple simulation of an 2D ideal gas, with elastic collisions. I wonder how should I simulate the pressure that is implemented on the particles in the box, by a piston with certain weight. it's easy to adjust the area of the box and the temperature of the particles which is proportional to the velocity squared, but I don't know how to change the pressure directly.

Thanks!

2. Oct 15, 2012

### mikeph

If the gas is ideal then you don't have the freedom to simultaneously control the temperature, pressure, volume and particle number- you may dictate three parameters, and the fourth will then be fixed according to the ideal gas equation: PV = nRT. In short, you can't arbitrarily change the pressure without losing control of one of the other variables.

Having said that, I'm intrigued about your simulation- surely if the gas particles are colliding elastically, then that breaks one of the ideal gas conditions: that the particles are non-interacting.

3. Oct 15, 2012

### leibo

Yes, you are right, it's a simulation of very simple real gas, rather than an ideal gas. I understand I can not decide the values of all 4 variables n,p,V,T. Yet, I can suddenly change T, with constant n, and V,P would change correspondingly to the equation. In the same way I want to be able to change the pressure P.

4. Oct 15, 2012

### mikeph

How do you mean "suddenly change T"? Are you arbitrarily changing the average kinetic energy? As a result of this the temperature and pressure will both change (at constant volume). To control the pressure, you can change T and keep everything else constant.