Energy in physics
Energy can be defined as the capacity or ability to do work and is measured by the amount of work a body can do.
Like work, energy is a scalar quantity. It can take on any forms. Energy is measured in the same unit as work, namely, joules.
In mechanics, energy is classified into two kinds kinetic and potential.
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Kinetic Energy:
Since energy is the capacity to do work, an object in motion must be endowed with energy. This is the kinetic energy of the object. Or kinetic energy is the energy which is possessed by a body by virtue of its motion.
Where m is the mass of the body and v is speed.
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Potential Energy:
Potential energy is the energy stored in a body or a system by virtue of its position in a field of force or by its configuration. Force acting on a body or a system can alter its potential energy. For example, the spring of a wound-up watch has potential energy because of the wound-up state or configuration of the coils.
As the spring unwinds, it does work to move the hands of the watch, i.e. the wound-up spring has the potentiality of doing work. An ordinary coil spring has the potential energy when it is compressed.
An object held at a position above the surface of the earth has potential energy by virtue of its position. When the object is released, it falls, thus acquiring kinetic energy. The potential energy of an object held above the earth is called gravitational potential energy.
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When an object falls from a height, it accelerates and gathers up speed, thereby gaining kinetic energy. This is at the expense of its gravitational potential energy. The total energy consisting of kinetic energy and the gravitational potential energy is conserved.
Conservation of Energy:
Whenever energy is transformed from one form to another or transferred from one body to another, it is found that no energy is lost in the process.
This is one of the most important principles of Physics and is called ‘the law of conservation of energy’ which states that ‘energy is never created or destroyed, it can simply he transferred from one form into another, but the total amount of energy remains constant.’