When work is done on an object, the object gains energy and the medium that does work loses energy. The amount of energy transferred is equal to the work done. It is not always equal to the amount of energy transferred to the object. Some energy is usually lost to friction and air resistance or as heat. This energy is lost forever.

Conservation of Energy

Though energy is usually 'lost' in the process of being transferred, it does not disappear. It is only changed into a form of energy which cannot be used to do something useful. In fact, energy is not lost in the sense that we do not know where it is gone. It is only changed into a form of energy – usually heat – that cannot be changed back into useful mechanical energy.

The principle of conservation of energy is one of the most fundamental laws of physics. It states that energy is never lost, destroyed or created out of nothing. The sum total of all forms of energy is constant. Energy can only be changed from one form into another. Some of these forms are useful and some of them are not. Some of them are useful at some times and not useful at others.

Types of energy include:

Kinetic () Gravitational () Electrostatic()Chemical Radiant Thermal or Heat (or) Nuclear Solar Elastic Potential () Electrical (or ) Internal (for a monotonic gas) Light (A photon has energy)

In the above expressions, where they occur,

andare point electric charges andis the distance between them

andare labels for temperature

is specific latent heat

is spring constant andis extension

is current,is Potential difference andis time

is Boltzmann's constant