P2 The gather of a plenty of events involves a kind of regularity. This is called statistical regularity. We’ll find that macroscopic state of the ideal gas can be related with the statistical mean of the microscopic state of the gas molecules.
This is the expression of a plenty of the gas molecules following statistical regularity.（6-1）
气体处于平衡态时，气体分子任何一个自由度上的平均能量都相等，均为 ，这就是能量按自由度均分定理。（P5） when the gas is in an equilibrium state, the mean energy of any gas molecule in a degree of freedom is equal to . This is known as equipartition theorem.（6-3）