Expansion

Expansion, in physics, increase in the volume of a substance due to a rise in temperature. Virtually all substances expand when heated, whether in a gaseous, liquid, or solid state. Conversely, they contract when cooled. Water, an exception, expands on cooling below 4°C (39°F), which is why ice floats on water. Expansion occurs because molecules move further apart as they vibrate more violently under the influence of heat. The increase in the length of a solid when it is heated by 1°C is called the coefficient of expansion. A bimetallic strip made of 2 metals with different coefficients of expansion is used in the thermostat. The expansion of mercury or alcohol is used to measure temperature in thermometers. Engineers must allow space for expansion when they build bridges, highways, buildings, railways, and any other structure subject to temperature changes.

See also: Physics.