When work is performed against inertia, and object's speed is changed. When work is performed against gravity, and object's height is changed. When work is performed against friction, heat is produced, and there is usually a change in the temperature. In all these examples something is changes when work is performed.

The idea of energy helps us to unify all the possible changes that occur when work is done. When work is completed, there is a change in energy. The amount of work done is equivalent to the change in energy.

Energy is one of the most crucial concepts in science. It is the quantity that is possessed by objects: when Work is done; objects have energy. When work is performed on a system, the amount of energy possessed by the system changes. Energy is the capability to do work or simply is stored work.

Fundamentally, work is the process by which energy is transferred from one object to another. An object with energy can do work on another object and provide it with energy. The amount of energy expanded is equal to the work done, so you should not be surprised to learn that work and energy have the same measuring units. In the SI system energy (and work) is both measured in joules.

Work and energy both has scalar quantities. That is, they don't have a direction associated with them. Thus various amounts of energy can be added and subtracted as numeric values. Forces can become difficult because of their vector or directional nature. In difference, energy, because it is a scalar quantity, is easy to use in computational problems.

Energy occurs in numerous forms. Two of the most crucial forms of energy are kinetic and potential energy.

KINETIC ENERGY

Kinetic energy, energy a body possesses because of its motion or, simply, is the energy of motion. As we learned, work requires motion, so when work causes a change in motion, there is a corresponding change in kinetic energy.

POTENTIAL ENERGY

Potential energy, the energy a body has because of its position or location or, simply, the energy of position. For example, if you hold a tennis ball in mid air, the tennis ball contains potential energy (it is ready to move once you let go of the ball, which means that it has the potential to move). But once you release the tennis ball from your hand, potential energy soon transformed to kinetic energy (the ball is falling to the ground, which is a energy of motion).

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