The coefficient of linear expansion is the fraction of its length that a body expands when heated one degree.
The coefficient of cubical expansion is the fraction of its volume that a body expands when heated one degree.
The expansion of solids is used or allowed for in many cases:
a. Joints between the rails on a railroad allow for the expansion of the rails in summer.
b. One end of a steel truss bridge is usually supported on rollers so that it can expand and contract with changing temperatures. (See Fig. 128.)
Fig. 128.—Truss bridge showing roller support at one end.
c. Suspension bridges have expansion joints where the ends of the iron girders can move in or out of an expansion joint thus making the bridge longer or shorter according to the temperature.
d. Iron tires are heated, slipped on to wagon wheels and then cooled, the contraction on cooling setting them tightly in place.
e. Metallic thermometers depend upon the movement due to the expansion of a coiled strip of metal which turns a pointer on the dial of the instrument. (See Fig. 129.)