“Conservation” is another word with different meanings in everyday speech and science.
English conservation is used to mean “saving for later,” in science conservation strictly means “not lost.”
When we say “energy is conserved” we mean all
of the energy before an event is accounted for after the
A second question comes up in our baseball example involving the catcher.
The pitcher converted
potential energy into kinetic; however, when the catcher did negative work to pull the kinetic energy out
of the ball, the catcher did not convert it into stored potential energy.
Where did the energy go?
According to the Law of Conservation of Energy, the energy extracted from the baseball still exists.
muscles contract and res
ist the ball’s forward motion, the muscle fibers rub against one another and
due to friction.
Other forms of energy may have also come out (sound from slapping the
mitt, deformations in the ball, etc.), and the total net sum of all their contributions must add up to the
original kinetic energy of the baseball.
Our bodies don’t have a mechanism for converting mechanical (or kinetic) energy
into stored potential
A spring could have stored the ball’s energy as it compresses, but even th
at amount would come
up “a little short” due to some slight heating.
Almost all energy conversions experience some inefficiency
not to be conserved.
We tend to make a distinction between energy that can do “useful work”
and energy that is “waste.”
In the analogy between energy and accounting, think about an energy
conversion as a purchase with some associated “tax.”