Importance of Joule’s work
When an account of Joule’s work became known in the middle of the nineteenth century it aroused but little interest, as the concept of work and energy was new to science. At the time it was not generally realized that Joule’s experiments provided
the first reliable experimental evidence for the truth of the principle of the conservation of energy.
This principle was put forward by the German physicist, Hermann von Helmholtz, in a book published in 1847, but it had earlier been accepted by other far-seeing scientists, particularly Sadi Carnot, Robert Mayer, and Sir William Grove.
The conservation of energy has already been discussed in chapter 7. Joule’s experiments had shown that internal molecular energy could be put into a substance by mechanical work and that there was an exact equivalence between these two forms of energy. Later it was demonstrated that the same exact relationship existed between other forms of energy, for example, electric energy, chemical energy, and heat. One can readily appreciate why Joule’s memory has been honored by giving his name to the SI unit of energy. Once the principle of conservation of energy had thus been established, the way became open for great advances in science. It formed the basis of a new branch of the study of heat and energy known as thermodynamics. Calculations could now be made regarding certain problems in physics with a certainty that the answer would be correct. In the field of applied physics the same can be said with regard to calculations on the design of steam turbines, internal combustion engines, rockets and jet engines, electric motors, generators, and power installations.