posted by anne .
I read in a book that gas particles move rapidly in all directions. Somehow I find that random directions is better.The word "all" sounds a bit weird. What do you think?
The word "All" is better. There can be a tendency to move more in one direction than another (if the gas is flowing), so the distribution is not truly (isotropically) random. Also, following a gas molecule collision, the distribution of velocities is not truly random. The molecules can go in all directions, but not with equal probability, on the average.
For a specific collision with a given impact parameter, the final velocities are deterministic and not random.