| HyperPhysics***** Thermodynamics | R Nave |
Many of the most fundamental arguments in physics are those having to do with multiplicity. If there are more ways to accomplish a given state of a system of particles, then other states will spontaneously transition to that state over time if the transition is consistent with conservation of energy. The multiplicity of a system of particles is stated in terms of its entropy. Systems will spontaneously proceed toward states with higher entropy (2nd law of thermodynamics). But what does that have to do with temperature?
Under conditions where the kinetic temperature as derived from kinetic theory provides reasonable accuracy, we perceive temperature as the average translational kinetic energy associated with the disordered motion of atoms and molecules. That makes it intuitive that the flow of heat is from a high temperature region toward a lower temperature region since higher energy molecules are striking lower energy molecules and transferring energy to them. Temperature is not directly proportional to internal energy since temperature measures only the kinetic energy part of the internal energy, so two objects with the same temperature do not in general have the same internal energy (see water-metal example). Temperatures are measured in one of the three standard temperature scales (Celsius, Kelvin, and Fahrenheit).
| Suppose we are dealing with two equal mass objects at ordinary temperatures and can presume that kinetic temperature gives a reasonable description of their behavior. If the two objects are at the same temperature, then we would say that their average translational kinetic energies are the same. That does not imply that their total internal energies are the same, because the potential energies associated with intermolecular forces can be quite different. |
Even if there are internal kinetic energies other than translational KE, it could be that heat transfer is mainly by collisional transfer. In such cases this picture might help understand that just a portion of the total internal energy of objects is involved in the conditions for thermal equilibrium.
Reference:
Schroeder
Ch 3
| HyperPhysics***** Thermodynamics | R Nave |