Thermal Expansion

Different materials expand or contract at different rates. In general, gases expand more than liquids, and liquids expand more than solids. Observation of thermal expansion in a solid object requires careful scrutiny. Several everyday examples are: 1) The sag in outdoor electrical lines is much larger on hot summer days than it is on cold winter days. 2) The rails for trains are installed during warm weather and have small gaps between the ends to allow for further expansion during very hot summer days. 3) Because the metal expands more than glass a stuck metal lid on a glass container can be loosened by running hot water over the joint between the lid and the container.

Liquids generally expand by larger amounts than solids. This difference in expansion rate is sometimes observed when the gas tank of a car is filled on a hot day. Gasoline pumped from the underground container is cold and it gradually heats to the temperature of the car as it sits in the gas tank. The gasoline expands in volume faster than the gas tank and overflows onto the ground.

Gases expand even more than liquids when heated. The expansion difference between a gas and a solid can be observed by filling a plastic air mattress in a cool room and then using it on a hot beach. The difference in thermal expansion between the container and the gas could unexpectedly over inflate the mattress and blow a hole in the plastic.