Degree of Freedom. What is the need for this concept?

We know that Temperature is the measure of Average Kinetic Energy of molecules of the gas. Greater is the temperature, greater is the average kinetic energy of the gas molecules. The kinetic energy of gas molecules can be due to several reasons. For example — If the gas molecule is diatomic then by the concepts of rotational dynamics, it can have translational kinetic energy, rotational kinetic energy and also vibrational kinetic energy. When average kinetic energies in all these dimensions are added together then we get the net total average kinetic energy of the molecule.

The next question which comes here is, why do we need to distribute the total kinetic energy of the molecule in various dimensions like translational, rotational and vibrational? Why can’t we just call it the net average kinetic energy?

The reason we need to distribute it is, “Law of Equipartition of Energy”. According to the Law of Equipartition of Energy, the total kinetic energy of a molecule is distributed equally, in all the independent number of ways it can possess kinetic energy, and the total number of independent ways in which a molecule can possess energy is called “Degree of Freedom”.

I will discuss the “Law of Equipartition of Energy” in the next article.

Next Article: The Law of Equipartition of Energy: Kinetic Theory of Gases.