# Time of flight

1. Oct 18, 2008

### h0dgey84bc

If one considers an ideal gas, what does the mean time between collissions of the molecules depend upon? molecular size? number per unit volume? temperature of the gas?

I'm thinking so far, it must def depend on number density. It would usually depend on molecular size (but I thought an ideal gas was supposed to assume point like particles?). It may not depend on temperature since n=PV/RT, so if you specifically number density then perhaps you already factored in temperature dependence?

Anyone know any specific formula for this mean time of flight or how to derive?

2. Oct 18, 2008

### h0dgey84bc

or perhaps it does depend on temperature because the particles have higher K.E and faster speeds on average?

3. Oct 20, 2008

### h0dgey84bc

bump

I'm thinking now time of flight only depends on temp not density or size for an ideal gas because they dont interact, and the temp is just entering into the v_rms for when they collide with walls is less?