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Q & A: thermal expansion

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Q:
What happen to the density of a body when temperature increases and decreases?
- angel (age 22)
singapore
A:
The most common effect is for bodies to expand when heated, giving lower density. At most temperatures, for example, water expands when heated. In the range from 0°C to 4°C it contracts when heated, as do some other materials.
"Heating" means letting in thermal energy, allowing the atoms or molecules to get to higher-energy states. Usually, those states have molecules spaced a little farther apart than the low-energy states. Sometimes, there's a cluster of low-energy states which have the molecules spaced a little farther apart (like the states in ice, which has more volume than liquid water) and in those cases heating can lead to contraction.

Mike W.

(published on 03/07/2008)

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