Rumford's Experiments on the Heat Generated by Friction

Benjamin Thompson, also known as Count Rumford, undertook a series of experiments into the heating effects of friction. His conclusions were published in an essay, “An Inquiry Concerning the Source of the Heat Which is Excited by Friction” was presented to the Royal Society in 1788.

When a metal cannon is made, a hole is bored into a solid piece of metal. The metal gets very hot. The origin of the heat was supposed to be caloric released during the boring process.

In a set of experiments, Count Rumford measured the temperature change as a result of bring a cannon with the appratus illustrated below.

Caloric being a fluid, it was supposed, it should have a mass, so if it were released, there should be a mass loss during the experiment, but the total mass of metal aster the experiment equalled the mass of matter before. If caloric were a substance, it should have no mass – what sort of substance could it be?

By surrounding the end of the cannon with a water filled box, and measuring the temperature rise during the boring process, he showed that a blunt cutting tool produced a very large heating effect. He collected the metal cut from the cannon, and showed this could not have been the source of the caloric. Further experiments allowed him to rule out the water and the rest of the machinery as the source of the caloric.

He was able to observe that the heat generated by friction seemed to be inexhaustible – at odds with the idea that caloric is a substance of which there should be only a certain amount. Apparently friction could create this substance, and as much of it as desired.

His conclusion was that heat was a form of motion. We now know bodies have heat because of the random kinetic energy of their constituent atoms and molecules.

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