We think of potential energy just as the name implies: the potential
to do something. Most of potential energy we view as being stored, like
in a spring. For example, a stretched spring has energy,
which is usually called elastic energy.
The spring
is made up of atoms which contain nuclei and electrons. The nuclei
and electrons exert electrical forces on each other. The work
done to stretch the spring is used to overcome the electrical
forces that hold the atoms close together. The energy of the stretched
spring can, in this view, be considered as electrical rather than
elastic in nature. It is potential energy because it exists in
the position of the particles relative to one another, rather
than in their speeds. As soon as the spring is released, the electrical
attraction of the individual atoms for one another causes them
to draw closer together, with the result that the spring snaps
together tightly. The potential energy changes to the kinetic
energy of the atoms moving closer together.
The energy in a uranium nucleus is potential energy, too, because
it is caused by the conditions in which the nuclear particles
exist rather than by the speed of the particles. When a neutron
collides with a uranium nucleus, much of the potential energy
of the uranium nucleus is changed to the kinetic energy of the
newly formed nuclei, of the extra neutrons, and of the radiation
that is given off.
Here's something you can try at home. Take a rubber band in between your
first finger and thumb. Don't stretch it just yet. Okay, now bring your
hand with the rubber band up to your forehead and press the rubber band
against your forehead without stretching it. Now pull your fingers apart
to stretch the rubber band. Did the rubber band change in temperature?
What you just did was an example of potential energy being converted into
heat energy. As the rubber band stretches, much of the potential energy
stored in the rubber band is given off as heat. That is what you feel on
your forehead.
