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Reading Selection, Lesson 5

Changing Temperature, Changing Density

Most matter increases in volume when it gets hotter. For example, if an iron rod is heated, it will get longer and fatter and its density will decrease. This happens because the mass of the rod stays the same, but its volume increases. The increase in the volume of matter with increasing temperature is called expansion. When cooled down, most matter decreases in volume and increases in density. This decrease in volume is called contraction.

A horse thermometer with a digital readout

This horse thermometer has a digital readout. Veterinarians can use it in conjunction with a computer. It does not use changing density to measure temperature. Do you know how it works?

A few substances behave differently when heated or cooled. Water is one such substance. When water approaches freezing, it expands and becomes less dense, which is why water pipes sometimes burst when they freeze and why icebergs float.

A thermometer with a dial readout

Some thermometers use bimetal strips to measure temperature. In this lesson, you may get some ideas about how these thermometers work.

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