Kinetic Theory Derivation: Why the One Third? | A-level Physics

How can randomly moving molecules produce steady gas pressure? Follow one molecule from an elastic wall collision to the kinetic-theory equation pV = ⅓Nm c_rms². We build the model from Brownian-motion evidence and its assumptions, calculate the momentum change and the same-wall round-trip time, then add the contributions of all the molecules. Isotropy explains the factor of one third. We finish with RMS speed, a worked pressure calculation and two scaling predictions. Lesson notes, practice questions, the ideal gas laws and the next lesson on temperature are linked below. 00:00 Why does a still gas exert pressure? 00:12 Pressure from molecular impacts 00:49 The ideal model 02:07 The same-wall round trip 03:01 From one molecule to the gas 03:34 Why the factor of one third? 04:15 RMS speed and the pressure equation 04:56 Worked example: find the pressure 05:45 How pressure scales https://inklearning.co.uk/physics/the... https://inklearning.co.uk/physics/pra... https://inklearning.co.uk/physics/the... https://inklearning.co.uk/physics/the... #ALevelPhysics #KineticTheory #InkPhysics