Coal has qualities that make it an ideal fuel. Compared to wood, coal burns at a higher temperature and produces more heat from the same volume of material. And while burning wood depletes forests, the supply of coal buried in the earth is so large that shortages have not yet been encountered after more than two hundred years of extensive use.

In a theoretical steam engine, a coal fire underneath the boiler heats the water, creating steam. The steam escapes through a valve into the cylinder, just underneath the piston, which is initially sitting near one end of the cylinder. As the steam continues to enter the cylinder, it pushes on the piston, forcing it toward the other end of the cylinder, and thereby pushing the rod attached to the top of the piston. Steam is quite powerful: the rod may be attached to a very heavy weight, which the force of expanding steam can also move.

Steam and Coal