Three types of molecular speed: (1) Most probable ($u_{mp}$) = sqrt$\frac{2RT}{M}$ = speed at peak of Maxwell-Boltzmann distribution. (2) Average ($u_{avg}$) = sqrt(8$\frac{RT}{piM}$) = arithmetic mean. (3) RMS ($u_{rms}$) = sqrt$\frac{3RT}{M}$ = root mean square. Ratio: $u_{mp}$ : $u_{avg}$ : $u_{rms}$ = 1 : 1.128 : 1.224 = sqrt(2) : sqrt$\frac{8}{pi}$ : sqrt(3). All speeds proportional to sqrt$\frac{T}{M}$. At higher T: distribution broadens, peak shifts right, all speeds increase. At higher M: all speeds decrease. Graham's law: rate of effusion proportional to 1/sqrt(M) (follows from $u_{avg}$ dependence).