This chapter is mostly quite straightforward. It begins with a discussion of the empirical meaning of temperature. This section also introduces the idea of thermal expansion.
``Heat'' is a verb, as in ``to heat''. It means to add to the energy of molecular motions of a body by molecular transfer processes such as heat conduction or absorption of radiation. ``Specific heat'' is the amount of heating needed to raise the temperature of a body of unit mass by one degree.
The first law of thermodynamics states that the change in internal energy (i. e., energy of molecular motion) of a body is equal to the heat added to the body minus the work done by the body. It is really a statement of the conservation of energy.
Heat conduction in a solid body obeys a simple law given in the text.
Thermal radiation is electromagnetic radiation emitted by the acceleration of charged particles which are undergoing ordinary thermal motions. The energy per unit area per unit time emitted by a body depends on the body's emissivity and its temperature. If the emissivity is epsilon, which ranges from 0 to 1, then the body has a reflectivity 1 - epsilon. Black body radiation occurs in a cavity where the walls are all the same temperature. This depends only on temperature and not on the emissivity of the walls.
Friction occurs when two bodies rub against each other. Friction between solids depends on the force holding them together and on the coefficient of friction. Be sure to understand the difference between static and kinetic friction. Friction between bodies separated by a thin sheet of fluid depends on the shear in the fluid and the fluid's viscosity.