Work and energy

When a force is moves something, work is done. And whenever work is done, energy is changed into a different form.

Work

In everyday language,work means almost anything that people do. In science; work is done whenever a force produces movement. The greater the force and the greater the distance moved, the more work is done.

The SI unit of work is the joule (J), which is defined as the work expended by a force of one newton through a distance of one metre.

The dimensionally equivalent newton-metre (N·m) is sometimes used as the measuring unit for work, but this can be confused with the unit newton-metre, which is the measurement unit of torque. Usage of N·m is discouraged by the SI authority, since it can lead to confusion as to whether the quantity expressed in newton metres is a torque measurement, or a measurement of energy.

Energy

Things have energy if they are able to do work. A human body has energy; so does a tankful of petrol or a compressed spring. In each case, you can think of energy as a promise of work to be done  in the future. Energy, like work, is measured in joules (J).

Energy exists in many forms:

In the context of physical sciences, several forms of energy have been defined. These include:

Kinetic

Potential, a category comprising many forms in this list

Mechanical, the sum of kinetic and potential energies

Chemical

Electric

Magnetic

Radiant, that of electromagnetic radiation including light

Nuclear, that of binding nucleons to form the atomic nucleus

Ionization, that of binding an electron to its atom or molecule

Elastic

Sound

Gravitational

Intrinsic, the rest energy equivalent to an object's rest mass

Thermal

Work-Energy Theorem:

The energy associated with the work done by the net force does not disappear after the net force is removed (or becomes zero), it is transformed into the Kinetic Energy of the body. We call this the Work-Energy Theorem.

                                                     

If the body's speed increases, then the work done on the body is positive and we say its Kinetic Energy has increased. Whereas if the body's speed decreases then it kinetic energy decreases and the change in kinetic energy DKE is negative. In this case the body does positive work on the system slowing it down or alternately the work done on the body is negative.

If the object is not rigid and any of the forces acting on it deforms the object, then the Work-Energy Theorem will no longer be valid. Some of the energy transferred to the object has gone into deforming the object and is no longer available to increase or decrease the object's Kinetic Energy.