Concept of Energy

 

Anything that has the ability to do work possesses some form of energy. A boy running along a race track possesses the energy to do so. A man pushing a car over a certain distance also possesses energy to move the car. Even a mango fruit which drops from the tree under gravity also possesses the energy to do so. These therefore implies that for a body to do work, it must have the energy to perform the designated task.

Definition of Energy

Energy can simply be defined as the ability of a body to do work.

 

Work and energy are inter-related and thus have the same unit which is the Joules. 

Forms of Energy

• Heat (or thermal) energy
• Mechanical energy
• Light energy
• Electrical energy
• Solar energy
• Chemical energy
• Atomic energy
• Nuclear energy etc.

We shall be limiting the scope of this lesson to mechanical energy.

Types of Mechanical energy

There are two types of mechanical energy which are; Potential energy and kinetic energy.

Potential Energy

Potential energy is the form of energy possessed by a body at rest. It is also known as stored energy because its a form of energy that is saved up to be used to do work when the body begins to move.

Examples of bodies that possess potential energy are:

• a stone on a table top
• a boy sitting still on a chair
• a magnet at rest in a magnetic field
• an electric charge lying at rest in an electric field

 A body may also possess potential energy due to its state or position in a force field e.g stone of mass, m lying on a table top of height, h above the ground level.

Its potential energy is thus calculated as ;

Potential energy = mass x acceleration due to gravity x height

                           = m x g x h

Kinetic Energy

Contrary to potential energy, kinetic energy is the energy possessed by a body in motion.

Examples of kinetic energy are;

• a boy running along a race track
• a mango fruit freely falling from a tree
• an electric charge moving in an electric field
• a moving bullet
• a bee flying from one flower to another.

Kinetic energy possessed by a body in motion can thus be calculated as;

K.E. = 1/2 mv²

where, m = mass of the body

            v = velocity of the moving body

Examples;

1. A mass of 5kg moves with a velocity of 2m/s. Find its kinetic energy.

Solution:

Kinetic energy = 1/2 mv²

                        =  1/2 x 5 x 2 x 2

                        =  10J

2. Find the potential energy of a man of mass 20kg sitting on a chair 5 metres above the ground level.

Solution:

Potential energy = m x g x h

                           = 20 x 10 x 5

                           = 1000J