TEMPERATURE MEASUREMENT (also
see Chapter 40
)
Principles of Temperature
Moving matter contains energy. Even stationary objects are moving
at the atomic level. This kinetic energy of molecules and atoms is described as
temperature. When all atomic motion ceases, the substance is said to be at absolute
zero. This state provides a reference point for all temperature measurements. Heat
has been defined as a form of internal kinetic energy that flows between two contacting
bodies at different temperatures.
The amount of heat required to raise the temperature of 1 g of
a given substance by 1°C is called the specific heat
of that substance. The calorie, a common heat unit, is the amount of heat required
to raise the temperature of 1 g of water from 14.5°C to 15.5°C. One calorie
is equal to 4.184 J. When we refer to calories in terms of the calories in the food
that we eat or the calories that we expend while exercising, we are actually referring
to kilocalories, or thousands of calories. The total amount of heat energy in an
object thus depends on its specific heat, its temperature, and its mass. For example,
although a cup of 60°C coffee is much "hotter" than a 30°C swimming pool,
the coffee contains much less total thermal energy than the pool does. The same
is true for potential energy stored as pressure potential or electrical potential.
A small container at high pressure may have less potential energy than a larger
container at lower pressure.
