## 1. INTRODUCTION

Learning through visualization of phenomena with the aid of simulations facilitates the understanding of abstract concepts such as heat, internal energy, temperature, entropy...

The aim of this unit is not the substitution of the textbook, but rather being a complement to it. The stress is on the computer simulation capabilities to carry out experiments that provide the user with an understanding that would require a larger abstraction effort by other means. The text is mostly reduced, trying to keep the selfconsistency in the development, and textbook reading are recommended when necessary.

This didactic unit is devoted to the introduction of the basic concepts in THERMODYNAMICS, such as heat, temperature, internal energy, work and entropy, from a microscopic point of view. Some of these words are employed in ordinary language with a different meaning from the scientific one, thus causing some difficulties when they are introduced to first levels students who are still not used to abstract concepts.

Thermodynamics is involved with the study of the macroscopic properties of matter arising from the fact that it is made of a very large number of particles. The basic concepts in THERMODYNAMICS will be introduced through a simulation of the simplest system: an IDEAL GAS that occupies a region of volume V.

An ideal gas is composed of a large number of particles that move continuously, suffering elastic collisions between them and with the container walls.

Collisions of the gas particles with the walls are at the origin of the pressure P. The sum of the energies of all particles is the internal energy of the system U. Another quantity characterizing the system is the temperature T, which is directly related to the average kinetic energy of a particle in the system.

The following sections are devoted to the definition of these quantities and the study of the relationship between P, V and T in an ideal gas. The concepts of heat Q and work W will be introduced later, leading to the statement of the First Law of Thermodynamics. Finally, the entropy S will be introduced as a concept related to the number of possible microscopic distributions of the system.

Pressure.

 Index 2.Pressure 3.Temperature 4.Internal Energy 5.Heat 6.Work. 7.First Law 8.Entropy 9.Velocity Distribution 10.Specific Heat