# Calculating the number of particles colliding with an area per unit time

1. Jan 24, 2012

### JDStupi

1. The problem statement, all variables and given/known data
Consider a small portion (area=A) of the inside wall of a container full of gas. Show that the number of molecules colliding with this surface in a time interval Δt is PAΔt/(2mvx avg), where P is the pressure, m is the average molecular mass, and vx avg is the average x velocity of those molecules that collide with the wall.

2. Relevant equations
PV=NkT, 1/2mv2=3/2kT, P=F/A=m(Δv/Δt)

3. The attempt at a solution

The problem here is that I am not entirely sure where to start and would appreciate some hints as to which way to proceed. I have attempted to see relationships between the Ideal Gas Law, temperature-KE equivalence, and the pressure but have yet to succeed. For those who are interested it is Problem 1.22a in Schroeder's Introduction to Thermal Physics.

Thank you very much for any hints and help

2. Jan 24, 2012

### ehild

3. Jan 25, 2012

### technician

If you start with the fact that P=F/A and that F = rate of change of momentum of colliding particles you should get an expression for P .
This expression should contain the details of number of collisions per second ,the change in momentum of each particle and the area A.
Hope this gets you started.