The derivation of the bulk properties of fluids from the properties of their constituent molecules, their motions, and interactions.
The average kinetic energy of N molecules in a gas is directly proportional to the absolute temperature:
kB = Boltzmann constant [JK-1]
m = molecular mass [kg]
vn = velocity of molecule n [ms-1]
T = gas temperature [K]
The speeds of molecules in a gas are distributed according to the Maxwell distribution.