Discussion of the Question 11/04
GAS OF ROTATORS
The question was:
Consider a very dilute gas of thin rodlike molecules. The kinetic
energy of such a gas is significantly larger than kinetic energy
of an ideal gas of point-like objects, because each rotational degree
of freedom has (on the average) kinetic energy (1/2)kT. Nevertheless,
the pressure of the gas is the same as of point-like molecules.
Show from dynamical considerations that the rotational degrees
of freedom do not contribute to the pressure.
(1/06) Y. Kantor: Some aspects of the problem have been solved by
Ioannis G. Florakis, from University of Athens, Greece
(e-mail
iflorakis@yahoo.gr).
His solution can be
found in the following PDF file.
He uses conservation laws to demonstrate that only the translational
degrees of freedom contribute to momentum transfer to the walls, and, thus,
to the pressure. He also provides an interesting discussion of what the
rotational degrees of freedom to the angular momentum of the surrounding
box. The discussion is not specific to the rods.
However, the collision between a wall an a rod can be descibed in detail.
Notice that a rod approaching the wall can collide with it several
times before moving away. We would like to see a detailed analysis of
such collisions.
Back to "front page"