Potential energy can be stored in a system, and then released
by a trigger, when and where we need it. Sometimes, the release
of the potential energy in a system can be initiated by adding
a small, initial amount of energy.
We need only push over the first domino in the row to start a
chain reaction that makes the whole domino chain fall down. Similarly,
the tiny spark produced by striking a match on the box triggers
a reaction that allows the stored chemical potential energy to
make the match burst into flame. In both examples, a small input
of energy is enough to overcome some threshold and trigger the
whole reaction.
However, a trigger is not always needed. Sometimes, we need only
to stop restraining an object with stored energy. For example,
by holding a raw egg over the kitchen floor, we can maintain its
gravitational potential energy. When we let go, it falls toward
the floor and its potential energy is transformed to kinetic energy
as it falls. A similar thing happens when we release the elastic
potential stored in a stretched spring by letting go of one end.
We didn’t have to give the egg or spring any more energy
to start a reaction. The energy was released as soon as we stopped
maintaining it in a stored, latent state.
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