"Energy
is defined as the ability to do work."
"Work is defined as the transfer of energy."
The
picture bellow shows water rushing downstream during a flood.
The water is said to possess kinetic energy since it is
moving. It gets this energy because it is falling through
a gravitational field. As it falls, energy in the gravitational
field comes out of storage and is used to move the water.
The water has energy, that is, kinetic energy, so, it has
the ability to do work. Work on an object occurs when a
force is applied to the object, and the object is displaced
as a result of the action of this force. This causes energy
to be transferred to the object. The water is doing work
on the plants and the soil on the banks of the creek. It
is pushing on the soil and forcing it downstream. The water
is also pushing, and thus uprooting, some of the smaller
trees and washing them downstream.
So, energy in the gravitational
field comes out of storage and is given to the water. This
energy is realized as the kinetic energy of the water. Since
the water has energy, it has the ability to do work. And
the water is doing work. It is placing forces on the soil
and the trees and washing them away. So, the soil and the
trees are having work done on them, that is, they are having
energy transferred to them. The energy transferred to them
shows up as their kinetic energy. They have this kinetic
energy since they end up moving as a result of work being
done on them.
