# Is F in P=F/A an average or a sum of all microscopic forces?

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1. Jan 13, 2015

### Greg777

Hello,
I've read that the force F we use in the pressure formula P=F/A is an average of all microscopic forces exerted by the gas on the wall of the container over a period of time. Is it true? I thought it was a SUM rather than an average?
I assume that in that definition the microscopic force is a force exerted by a SINGLE particle on the wall.

2. Jan 13, 2015

### Matterwave

It's a sum over all the different particles, but an average over time. When the text talks about averaging, it should be talking about averaging over time to smooth out the random fluctuations of collisions with particles.