10 - Heat and Thermodynamics

Abstract

This chapter explains heat and thermodynamics. The physics of thermal phenomena is a treatment of certain relationships among macroscopic, measurable quantities that are fundamentally microscopic in nature. The basic principles of thermal physics are known as the laws of thermodynamics. Matter is composed of microscopic particles that are in continuous random motion. This chaotic movement, which is called thermal motion, is exemplified by a gas. Relatively high speeds and extremely high collision rates characterize this highly chaotic molecular motion. The relationships between the macroscopic variables that reflect what is taking place at the microscopic level are collectively called thermodynamics. A thermodynamic system may, in general, interact with other systems or with any part of the remainder of the universe that is external to that system. An isolated system is a well-defined set of particles that does not exchange energy with the universe external to that system. When the two bodies reach thermal equilibrium, their final common temperature is intermediate between their original temperatures. The energy that is transferred between bodies because of their temperature difference heat energy or simply heat. Heat, thermal energy in transit, may be measured using any unit associated with energy, but the standard unit of heat is the calorie.