Microscopically, the size of molecules can be ignored compared with the distance between them. Except for collisions, the intermolecular forces can be ignored.

Dadong Xili studies the aerodynamic theory, regarding gas as an ideal gas, and molecules are rigid, ignoring the interaction between molecules. Potential energy is zero.

When considering the speed of molecular motion, all directions in the spatial coordinate system should be considered. In addition, the pressure at one point has nothing to do with the direction of the position.

The research object is ideal gas. The derived formula is also an ideal gas in an ideal state.