84 The Poetry of Physics and The Physics of Poetry
a model for the erroneous concept that heat is a conserved quantity. Heat
was considered to be weightless fluid called caloric. The transfer of heat
from a warm body to a cool body involved the flow of the fluid caloric,
which was conserved. The generation of heat as a result of friction would
appear to contradict the idea that heat was a conserved fluid.
The generation of this heat was explained however, as arising from
caloric being squeezed out of the body by the action of the friction. This
would mean that only a fixed amount of heat could be generated from
any given body due to friction for once all of the caloric had been
squeezed out of the body, it would have no more heat to give. Count
Rumford (nee Benjamin Thompson) in 1790 or thereabouts, while
working in a cannon factory observed a direct contradiction of this idea.
He noticed that an inordinately large, almost unending, amount of heat
was generated in boring the hole necessary to convert a large metal rod
into a cannon.
Further study quickly revealed that he could generate as much heat
through friction as he wanted, as long as he provided the necessary work
to generate the friction. You can perform this experiment yourselves by
rubbing your hands together. The only limitation on the amount of heat
you create will be the physical exhaustion you experience from rubbing
your hands together. Count Rumford discovered that the amount of heat
is not conserved and that the creation of heat requires work.
Heat is also generated when a moving object suddenly comes to rest.
For example, if a ball falls to Earth, the temperature of the ground and
the ball increase immediately after the ball strikes the ground and comes
to rest. In both the example of friction and the falling ball motion is
converted into heat. An understanding of these processes involves the
realization that the heat of an object is nothing more than the internal
motion of the atoms of which it is composed. Motion is converted into
heat simply because the external motion of the object is converted into
the internal motion of its atoms. Work is converted into heat by first
creating motion, which in turn is changed into heat. The connection
between work and motion is quite obvious. It takes work to create
motion. A horse must work to pull a cart. It takes work to lift an object to
a certain height in order to give it motion by dropping it.
The above discussion illustrates the equivalence of heat, motion and
work. It is the concept of energy that ties together these three quantities,
for it requires energy to perform work, to create motion or to generate
heat. The term energy comes from ancient Greek word energos, which
meant “active working”.