What thermal expansion is
Two glasses washed and stacked one inside the other sometimes stick fast. Pour cold water into the inner glass and stand the outer one in hot water, and they come apart easily.
Figure to be added
The hot water makes the outer glass slightly larger and the cold water makes the inner one slightly smaller.
Thermal expansion
The increase in size — length, area or volume — of a substance as its temperature rises.
Contraction
The decrease in size of a substance as its temperature falls.