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© NOAA:
Jetstream Online
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Air consists of gas molecules, which are
constantly moving this way and that at very high speeds.
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Air consists of gas molecules, which are combinations of two or more
atoms. Although you cannot see them with your eyes, the molecules are
constantly moving this way and that at very high speeds. As they move,
they collide with one another and with solid surfaces. The temperature
of the air is a measure of how quickly the molecules are moving. The more
energy of motion the molecules have, the higher the temperature you feel
in the air.
Air temperature is measured with thermometers. Common thermometers consist
of a glass rod with a very thin tube in it. The tube contains a liquid
that is supplied from a reservoir, or "bulb," at the base of
the thermometer. Sometimes the liquid is mercury, and sometimes it is
red-colored alcohol. As the temperature of the liquid in the bulb rises,
the liquid expands. As the liquid expands, it rises up in the tube. The
tube is marked with a scale, in degrees Fahrenheit or in degrees Celsius.
When you are measuring the air temperature, be sure to have the thermometer
in the shade. If the sun shines on the thermometer, it heats the liquid.
Then the reading is higher than the true air temperature. Also, when you
take the thermometer outside, give it enough time to adjust to the outdoor
air temperature. That might take several minutes.
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