Energy

Energy of a body is defined as the capacity or ability of the body to do Work.

Mechanical energy
It includes kinetic and potential energy. Kinetic energy The energy possessed by a body by the virtue of its motion is called kinetic energy. An object in motion has the ability to do work and hence possesses kinetic energy.

Examples of Kinetic Energy

(1) Wind possesses kinetic energy and can run wind mill.

(1) The kinetic energy of flowing water is used to generate electricity.

(ii) A bullet fired from a gun possesses kinetic energy and can penetrate a target.

Formula Kinetic energy = 1/2 *mv² Where m = mass and v² = velocity squared

Potential energy The energy possessed by a body by the virtue of its position(displacement) or its configuration (shape or size) is called potential energy. An object may have the capacity of doing work as a result of its position in a gravitational(gravity) field, an electric field or a magnetic field. Potential energy may be positive or negative. Potential energy is often referred as stored energy.

Examples of Potential Energy

(1) The heavy ball of a demolition machine has potential energy when it is held at an elevated position.

(i) A stone lying on the ground has no energy so it cannot do any work. If this stone is lifted to the roof of a house, the work has been done in lifting this stone against the force of gravity. This

work gets stored up in the stone in the form of potential energy.

(ii) The water stored at height in a dam has potential energy. If it is allowed to fall, the falling water has the ability to rotate turbine to generate electricity.

(M) A stone resting on the edge of a cliff has potential energy due to its position in the earth's gravitational field. If it falls, the force of gravity which is equal to the stone's weight will act on it until it strikes the ground. The stone's potential energy is equal to the product of its weight and distance it can fall through.

(1) Elastic Potential Energy

The energy possessed by a body due to the change in its shape is called as elastic potential energy. The change in shape of the body can be brought by compressing, stretching or bending. For this change, some work has to be done. This work gets stored in the form of elastic potential energy. When this deformed body is released it regains its original position and potential energy is given out in some other form of energy. (B) "The gravitational potential energy of an object at a point above the ground is defined as the as the work done is raising it from the ground to that point against gravity without any acceleration"

Formula Work (w) = Mass (M) * Gravity (g) * Displacement (S) or w = mg * s

Potential energy = mg * h

Heat energy
Heat can be defined as the form of energy that is transferred between two points due to the presence of a temperature difference between the two points. When water boils, it changes to steam. The steam possesses heat energy because it has the ability to do work such as to run stear engines, turbine etc. The heat produced by the burning of petrol in a car engine provides the energy needed to run the car.

Nuclear energy
The energy stored in the nucleus of an atom is called nuclear energy. The energy stored in the nuclei of atoms can be obtained by carrying out two types of nuclear reactions called nuclear fusion and nuclear fission.