### ASA 127th Meeting M.I.T. 1994 June 6-10

## 3aED3. Computer graphic simulations of microscopic particle collisions for
determining macroscopic thermodynamics along a path.

**Devin P. Espindle
**
Murray S. Korman

**
**
*Dept. of Phys., U.S. Naval Acad., Annapolis, MD 21402
*

*
*
The heat absorbed by an ideal monotomic gas during an isothermal
expansion---when a piston slowly moves from volume point V[sub 1] to V[sub 2]
in a cylinder---is a standard problem in thermodynamics. Students taking the
SP226 Heat, Light and Sound course learn that the process involves (a) an
understanding of the kinetic energy loss that a gas molecule makes with the
slowly moving piston ``called the bunt,'' (b) the drop in internal energy of
the gas as a collection, which leads to a slight drop in temperature of the
gas, and (c) the transfer of heat from the reservoir to the gas until an
equilibrium temperature is reached. This problem is modeled in two dimensions
on a computer. The collisions involve N elastic scatterers that each have a
cross section of radius r[sub 0]. The heat resevoir is modeled by molecules
having a random distribution of velocities at the wall boundary which is in
contact with the gas. The piston is modeled as a wall which moves at the speed
V[sub wall]. Thermodynamic calculations involving work, heat and entropy are
attempted for the model system. Adiabatic and free expansions are also
simulated and compared with the well-known theoretical results. Work is
extended to cover collisions involving intermolecular potentials.