The bases of modern science / by J.W.N. Sullivan.

  • Sullivan, J. W. N. (John William Navin), 1886-1937.
Date:
[1939]
Catalogue details

Licence: In copyright

Credit: The bases of modern science / by J.W.N. Sullivan. Source: Wellcome Collection.

    83/260 (page 73)
    is constant. Energy may take new forms, but it cannot be created or destroyed. Thus, as Joule’s experiments showed, the energy of a falling weight can be converted into heat. Conversely, heat can be converted into mechanical work, as in the case of a steam-engine. Again, the energy of motion of moving water or moving air can be diverted and made to reappear in another form, as in the case of a water-mill or wind-mill. The energy of strain stored up in a bended bow appears, when the string is released, as the energy of motion of the flying arrow. Energy that vanishes in one form reappears in another, and the principle asserts that the quantity of energy in the universe, like the quantity of matter, is constant. But in order that the total amount of energy in the universe should remain constant it is necessary to invent the concept of “ potential ” energy. A stone let fall from a height, for example, acquires velocity and therefore energy of motion. On striking the earth this energy is transformed into heat. But where does this energy come from ? It would appear that energy can be created merely by letting a stone fall. The principle of conservation is preserved, in this case, by saying that the stone, before it fell, possessed “ potential ” energy. Owing to the relative positions of the stone and the earth the stone has a latent capacity for doing work. Thus a stone on top of a mountain has more energy than an exactly similar stone at the foot of the mountain. As the stone falls it loses potential energy and acquires energy of motion, or kinetic energy. It is the sum of