How Joule's Mechanical Equivalent of Heat Experiment Changed Our Understanding of Temperature

James Prescott Joule's apparatus. Credit: Harper's New Monthly Magazine, No. 231, August 1869

By Andrew Bennett

For many years, people did not understand the nature of temperature. In an experiment that combined measurements of motion (and the energy associated with it) and temperature, James Prescott Joule established that the energy associated with motion and position is the same as the energy associated with heat.

Richard Feynman had a great way of describing how all this works at the atomic level. Check out an interview where he describes atoms "jiggling" and how we perceive it as temperature.

How Do We Apply the Results of Joule's Experiment?

This establishes some key ideas for our investigations of processes involving compressing, expanding, heating, and cooling of gases.

At the end of this video, we work through a conservation of energy problem that has energy entering or leaving the system both as work and as heat.

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