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Temperature Conversions

Temperature is a measure of a molecular motion

Air temperature is one of those things that everyone is familiar with that's more complicated than it might seem at first. What thermometers actually measure is the average kinetic energy of air molecules that surround it. Air molecules in colder air move slowly compared to the molecules in warmer air. The kinetic energy of an air molecule is directly proportional to the velocity of the molecule. As a result, colder air has less kinetic energy than warmer air. When air molecules collide with a thermometer, kinetic energy is transferred from the air molecules to the glass and then to the mercury molecules inside the thermometer. As the mercury molecules begin moving faster they move farther apart, pushing the mercury up in the thermometer. In colder air, the energy from the air molecules colliding with the thermometer transferring to the mercury molecules is less than the energy from warmer air. As a result, the mercury molecules move slower in the colder air and the mercury inside the thermometer does not expand as far up the tube as it does in the warmer air.