If someone asks you for the temperature, more often
than not, you would respond with the degree or the “feel” of the
temperature (hot, warm, or cold). We usually have a good feel for how a
temperature is qualitatively different than another temperature. The
dictionary has many definitions for temperature, such as: “the degree of
hotness or coldness of a body or environment” and “a measure of the
warmth or coldness of an object or substance with reference to some
What is temperature really measuring? Some numbers
on a thermometer? There is definitely more to it than that.
For a better understanding of what temperature
really is, we need to review kinetic energy again. Kinetic energy is
defined as the energy of motion. An object, or a particle, that is
moving has kinetic energy, and includes three common forms--vibrational
(motion possessed by an object that is vibrating about a fixed
position), rotational (associated with an object that is rotating about
an imaginary axis) and translational (movement of an object from one
place to another).
The scientific definition of temperature is a
measure of the average kinetic energy of the particles in a sample of
matter. A sample of matter consists of particles that can be vibrating,
rotating and moving through the inside of its container. At the particle
level, a sample of matter possesses kinetic energy. A cup of hot
chocolate on a countertop may appear to be as still as can be, but it
still has kinetic energy.
At the particle level, there are atoms and
molecules that are vibrating, rotating and moving through the inside of
the cup. Stick a thermometer in the cup and you will see evidence that
the hot chocolate possesses kinetic energy. The hot chocolate’s
temperature, as reflected by the thermometer’s reading, is a measure of
the average amount of kinetic energy possessed by the molecules.
When the temperature of an object increases, the
particles that make up the object begin to move faster. Increasing the
temperature of an object causes an increase in particle speed. So as a
sample of water in a pot is heated, its molecules begin to move with
greater speed, and this greater speed is reflected by a higher
thermometer reading. Likewise, if a sample of water is placed in the
freezer, its molecules begin to move with a lower speed and this is
reflected by a lower thermometer reading. In this sense, a thermometer
can be thought of as a speedometer!