Random Molecular Motion

Kinetic theory: gas molecules are in constant random motion, colliding elastically with each other and walls.

Random direction at any instant; speeds follow a Maxwell-Boltzmann distribution.

Brownian motion (1827): tiny particles suspended in fluid show random jiggle — direct evidence of molecular collisions.

No preferred direction in a gas at equilibrium — isotropic.

Average velocity of a gas at rest = 0 (vectors cancel). Average SPEED ≠ 0.

Diffusion: net transport of molecules from high to low concentration due to random motion.

Effusion (Graham's law): rate of effusion ∝ 1/√M — lighter gases escape faster.

Random walks: in time t, average displacement scales as √t (not t).