# Energy Conversion and Law of Conservation of Energy with Examples

In this blog, we are going to learn about energy conversion and the law of conservation of energy with examples.

We know that energy is available to us in various forms such as:

1. Mechanical energy
2. Electrical energy
3. Heat energy
4. Light energy
5. Sound energy
6. Chemical energy
7. Nuclear energy etc

The various forms of energy are inter-convertible.

Robert Mayer stated that “Energy can neither be created nor be destroyed, it can only be converted from one form to another and as such, the total energy in this universe remains constant”. This is called the law of conservation of energy, which was later established by Helmholtz in the year 1842.

The loss of energy of one system is exactly equal to the gain of energy of the other system. This law is true for all situations and for all kinds of transformations. There are many such examples of energy conversion.

Energy Conversion

Conversion of mechanical energy to electrical energy:-

In this, the potential energy of water stored in the dam is changed to kinetic energy when it falls from the height. The kinetic energy of water rotates the turbines to produce electrical energy. When we stretch a bow, the potential energy gets stored in the bow due to a change of shape and then this energy is then used in the form of kinetic energy in throwing the arrow.

When we lit an electric bulb, electric energy is converted into light energy. When we use a loudspeaker, electrical energy is converted into sound energy. When we switch on an electric fan, the blades of the fan start rotating as electric energy is converted into kinetic energy which is actually a form of mechanical energy. When we charge a battery, electrical energy changes into chemical energy. A solar cell converts light energy into electrical energy.

Let us understand the Law of conservation of mechanical energy of a freely falling body. Here we will neglect the effect of air resistance on the motion of the body.

Let us consider a body of mass “M” placed at a point ‘A’.

‘S’ is the distance of any point C from ‘A’
g is the acceleration due to gravity at that place.
v1 is the velocity of the body at point C.
v2 is the velocity of the body at point B, a point just above the ground.
h is the distance of the body between the initial & final points.

At the point A

The velocity is Zero i.e. u =0
Potential Energy EpA = mgh
Kinetic Energy EkA = 0

Total mechanical energy = EA = EpA + EkA = mgh + 0 = mgh

At the point C

When the body moves from A to C , it covers a distance S

Let the velocity at point C = v. Using the equation of motion we know that
V2-u2 = 2as
Then v2– u2 = 2aS
This implies v2-0 = 2gs

Now, Kinetic energy at point C
EkC = ½ mv2 = ½ m(2gS) which is equal to mgS

Now, Potential energy at point C
EpC = mg(h – S)

Thus the total mechanical energy at point C is given by:-

EC = EpC + EkC = mg(h – S) + ½ m(2gS) = mgh

Now let us calculate the total mechanical energy at the point B

From the equation of motion we have,
v2-u2 = 2as

Here u is equal to zero because the velocity at the starting point A is zero, this implies

v2-0 = 2gh

Thus Kinetic energy at point B i.e. EkB = ½ ( mv2) = ½ m(2gh)

Thus potential energy at B
EB = EkB + EpB =mgh
Thus from above we can observe that EA = EB = EC

The total mechanical energy of the body at all points A, B, and C is the same. Thus, the mechanical energy of the body throughout the free fall is conserved. As the body falls down, the potential energy goes on decreasing, whereas the kinetic energy goes on increasing.