"Energy is the
capacity to do work."
"A vegetable is a potato."
"Energy can be unavailable
for doing work."
"A vegetable might not be a potato."
Energy is necessary
for doing work, but something else is needed, too. There's a trouble
maker lurking about which can render energy unavailable for doing work.
That essential "something else" is that we get rid of the trouble maker.
"trouble maker" is entropy.
There's another kind
of trouble maker here too, but this is one that occasionally lurks in the
logic we use. It's the confusion of necessity
To define energy as "capacity to do work," we must show both necessity
and sufficiency. However, while energy is necessary for doing work,
it is not
sufficient. Those textbook authors who define energy as capacity
for doing work are making the logical error of confusing necessity and
sufficiency. (That's an improperly
short lecture, with exemplar; ("Back" to return).
One person might easily
sense when this error is being made; another person might not. Meet
one of each; ("Back"