How Thermometers Work
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||grades 5 to 8
||Flesch-Kincaid grade level:
||inaccurate, ometer, therm, thermometer-making, metric, finding, based, mounted, opposite, alcohol, inventor, scientist, decimal, backboard, boils, liquid
||United States, Galileo Galilei, Ferdinand II, Grand Duke
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How Thermometers Work
By Cindy Grigg
1 How hot is it outside? How cool will it be tonight? Do you have a fever? The way we answer these questions is by using a thermometer. People are always interested in measuring things, so it is not surprising that a device was invented to measure temperature. It is called a thermometer. "Thermo" means heat, and "meter" means a measuring device. Some of the things we measure are the temperature of the air, the temperature of our bodies, and the temperature of food when we cook. Temperature is a measure of the amount of heat, or thermal energy, generated by the particles that make up an object.
2 Did you ever wonder how a thermometer works? A thermometer has a glass tube sealed at both ends and is partly filled with a liquid like mercury or alcohol. As the temperature around the thermometer's bulb heats up, the liquid rises in the glass tube. The glass tube is mounted on a backboard that is marked in units called degrees. When it is hot, the liquid inside the thermometer will expand and rise in the tube. The opposite happens when it is cold. The temperature on a thermometer is read by finding the level of the liquid in the tube and the number on the temperature scale across from it. The temperature is written in numbers with the (degree) sign. For example, 70 F is read: 70 degrees Fahrenheit.
3 Alcohol is a good liquid to use in a thermometer because it remains a liquid over most of the normal temperatures found on the Earth's surface. You will sometimes use alcohol thermometers in school. The alcohol is often colored red or green so that the liquid can be seen more easily. However, alcohol is not much use at hot temperatures because it boils at about 80Celsius (176F), which is too a low temperature for many things to be measured with an alcohol thermometer. For higher temperatures, a different liquid is needed, so mercury is used.
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