 Chris Fox's Engineering Section

Heat and Energy

Energy (E) is the capacity to do work. Work (W) is defined as the operation of a force over a distance, and its value is obtained using the formula W=Fd. The SI unit of both energy and work is the joule (J).

There are many forms of energy, including heat, light and chemical energy. For the purposes of science, however, energy exists in only two distinct forms: potential (stored) and kinetic energy. The total amount of energy in a body consists of these two forms. Chemical energy in food is potential energy. An object at height possesses gravitational potential energy. A stretched spring has spring potential energy. Kinetic energy is the energy a body possesses due to its motion; its value is equal to 0.5mv², where v=velocity.

Heat naturally flows from a hotter body to a colder one. There are three modes of heat transfer: conduction, where heat is transferred through a body without the net flow of matter; convection, where heat transfer involves the motion of a fluid; and radiation, where heat is transferred in the form of electromagnetic rays. More than one of these may take place simultaneously.

Thermodynamics, literally meaning "the movement of heat", is concerned with the relationships between heat and other forms of energy. Its laws are empirical but have been shown to apply generally, with no recorded exceptions. There are four such laws; these are numbered 0 to 3, instead of 1 to 4, because the Zeroth Law was discovered after the First Law but is more fundamental.

One reason why the material in this chapter is of interest to the engineer is because, as will be seen elsewhere in this section, temperature affects both the properties of materials and the deformation of bodies.

[Systems and Properties] [Temperature] [Energy Transfer] [Ideal Gases] [Phase Changes: Liquid to Vapour] [Cycles] [Second Law of Thermodynamics] [Heat Transfer] [Conduction] [Convection] [Natural Convection] [Forced Convection in Internal Flows] [Forced Convection over Various Bodies] [Radiation] [Heat Transfer in Boiling]