Assumptions
- There are a very large number of molecules (N)
- Molecules have negligible volume compared to the container
- The molecules show random motion (ranges of speeds and directions)
- Newton’s Laws of Motion can be applied to the molecules
- Collisions are elastic and happen quickly compared to the time between collisions
- There are no intermolecular forces acting other than when they collide
The Big, Bad Derivation
The molecules move in all directions. Let us start with one molecule of mass m travelling with velocity vx. It collides with the walls of the container, each wall has a length of L.