Physics for Geologists, Second edition

Heat and heat flow
The noun heat has several different meanings:
the quality of being hot, as in a heat wave;
the perception of this quality;
the quantification of this quality, for example, temperature.
Heat is a form of energy and can do work (hence the dimensions) and it
is conserved. Bodies have an internal energy due to their heat, and heat
cannot flow from a cold body to a hot body without an input of energy.
Temperature [ L~T-~] in dynamical units, or 0 in thermal units, is a measure
of the hotness of an object or material, but it is not a measure of the amount
of heat [ML~T-~] in the object or material. This must depend on the size
and the nature of the object. It takes more heat to raise the temperature of
two litres of water from 20°C to 100°C than it does for one litre; and if
you add the litre at 100°C to the two litres at 100°C you have three litres at
100°C. Temperature is a measurement of heat per unit of mass. Table 7.1
lists the quantities we are mostly concerned with in geology.
Heat can be transferred. If you sit in front of a fire, you can feel its heat.
A steak is heated under a grill. This is radiated heat, and the process is radiation
(yes, some radiation is beneficial!). As you solder a wire, the heat moves
along the wire towards your fingers and they feel heat. This is conducted
Table 7.1 Heat: common symbol, units and dimensions
Quantity of heat
Temperature
Q
T, 0,0
J
K, "C
Heat flow rate Q, W
Density of heat flow rate q W mP2
Heat capacity C J K-'
Specific heat capacity c J kg-' K-'
Thermal conductivity X, k W m-' K-'
Thermal gradient A011 "C m-'
Copyright 2002 by Richard E. Chapman
Symbol Unit Dynamical Thermal