A steam locomotive is a machine that propels itself and other vehicles by means of the expansion of steam. [1]: 80 It is fueled by combustible material (usually coal, oil or, rarely, wood) which is burned in the firebox to heat water in the locomotive’s boiler into steam. As a gas, the waters volume is 1,700 times greater than as a liquid! In most locomotives, the steam is admitted alternately into each end of the cylinders to move the pistons back and forth. This lateral motion (or reciprocatin