# The Physics Department - Mechanics, Energy

Energy is defined as the ability to do work.

Work is defined as the transfer of energy.

The picture above 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.

Energy is defined as the ability to do work.

Work is defined as the transfer of energy.

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