Thermal expansion
tendency of matter to change volume in response to a change in temperature
Thermal expansion is the tendency of matter to increase in size with increasing temperature. Matter generally increases in length, area, and volume, changing its size and density, in response to an increase in temperature (usually excluding phase transitions). Substances usually contract with decreasing temperature which is called thermal contraction. The SI unit of thermal expansion is the inverse kelvin (K−1).
Temperature is a measure of the average kinetic energy of the molecules in a body. The faster the molecules are moving, the higher that body's temperature is. Specifically, it is a monotonic function of the average molecular kinetic energy of a substance. As the energy in the particles increases, they start moving faster and faster, weakening the intermolecular forces between them and therefore expanding the substance.
When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between them.
The relative expansion (also called strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion.
The public source identifies “Thermal expansion” as tendency of matter to change volume in response to a change in temperature. This brief keeps that definition visible, then builds a research path around Thermal, expansion and tendency.
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This entry incorporates text from “Thermal expansion” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.