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Rap
Rap is offline
#17
Mar15-12, 03:51 PM
P: 789
Quote Quote by Philip Wood View Post
A molecule hitting the wall does exert a (varying) force over a very small time interval. How could it not do so? When it comes to calculating the mean pressure on the wall (that is the observed pressure) it is, as Rap nicely explains, the momentum change of the molecules which we use, not the forces of single particles.
That's right - the molecules do exert a force over a very small time interval. What I should have said was that the size of that force and the duration of that time interval isn't really what's important, its their product that's important, which is equal to the momentum that they transfer. That's because the time interval we are averaging over is many, many times bigger than the collision time interval.