Probably Not, 2nd Edition

17Statistical Mechanics and Thermodynamics

Introduction

This chapter will present a very brief, nonmathematical, introduction to a field of science that is based entirely on the laws of probability and statistics. However, in most situations, the concepts of probability that we have been dealing with, such as mean, standard deviation, and confidence interval, are never mentioned. Since this science is central to how our world works, it was felt that this chapter is relevant and belongs in this book.

Our macroscopic world is made up of atomic and subatomic particles. The interactions between these particles result in what we see, hear, and touch. Gases are an important subset of these particles; gas molecules have simple individual properties (mass, velocity). However, when we are dealing with billions or more molecules of gas at once, mechanical analysis of a system is out of the question; we must deal with the statistical properties of a macroscopic volume. Two of these properties, which arise from statistical analysis, are commonly known as temperature and pressure¹; in other words, the statistics of gases is the study of heat and heat flow, which in turn leads to the study of thermodynamics. The laws of thermodynamics teach us, among other things, how we can and cannot get useful work out of heat engines such as the internal combustion engine.

The air around us is made up of many, many, molecules of gas, all moving around randomly (Brownian motion). These molecules collide, ...