Many natural phenomena, familiar in everyday experience, are described and explained by the branch of physics called thermodynamics. Indeed the entire subject of thermodynamics began with a study of the basic properties of heat (steam) engines, whose development brought about the industrial revolution. In fact, everyday questions such as "What makes ice skating possible?" or "Why is the pressure in the tires higher right after driving?" can also be addressed by applying the laws of thermodynamics. In general, the laws relating the macroscopic quantities (which include pressure, volume, temperature, internal energy and entropy) form the basis of the science of thermodynamics.
Complementary to thermodynamics, a branch of physics called statistical mechanics exploits the fact that all matter is constructed from atoms. Note, however that the laws of thermodynamics do not rely on this fact. Statistical mechanics addresses the same area of nature as thermodynamics. The basis of statistical mechanics are the laws of physical mechanics (Isaac Newton's1 laws of motion), applied to the individual atoms that make up the system.
The number of atoms in a typical macroscopic sample of gas is on the order of 1023. No computer can solve the problem of applying the laws of mechanics individually to each and every atom in this gas. Instead, we can apply the laws of mechanics statistically. Using statistical methods, the large number of atoms in the system actually becomes an asset in determining the average values of thermodynamic variables.
One of the ways to apply the laws of mechanics to an assembly of atoms is using kinetic theory. This approach can be applied in an intuitive way, using statistical averaging techniques. In this approach, atoms are treated like billiard balls and their motion is described by Newton's laws of motion. Despite this simplistic view, the kinetic theory of matter is successful enough that it firmly established the atomistic view of matter near the beginning of the twentieth century.