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Potential Energy

The potential energy of an object in this case is given by the relation:

PE = mgh joule


  • PE = potential energy (in Joules)
  • m = mass (in kilograms)
  • g  = acceleration due to gravitational of the earth (9.8 m/sec2)
  • h  = height above earth's surface (in metres)

Let us understand what potential energy is by taking some examples.

(a) During an avalanche or landslide, huge rocks and boulders come rushing down the mountain side and destroy objects lying below. Before the landslide, these rocks were at rest on top of the mountain.


How did they possess so much energy to cause such a destruction? 

Will the destructive effect be more if the rock falls from a lesser height or from a greater height? Will the destruction be more, if the rock was massive or small?


(b) Ranjit places an arrow in the bow and stretches the bowstring. When he releases the bowstring, the arrow shoots forward and hits Madhu who gets hurt.

Will the arrow hurt Madhu more, if Ranjit had stretched the bowstring only a little or if he had stretched it very much?

In (a), when the stone was at rest on top of the mountain, it had energy stored in it. This energy was used to do work when the stone fell down. The stone possesses energy because of its height above the ground.

In (b), the stretched bowstring, though at rest, has energy stored in it. When the bow is released, this energy is used to do work to push the arrow forward. The stretched bowstring possesses energy because it is deformed.

In the examples discussed above, the stone and bow are both stationary but still they possess energy.

The energy that a stationary object possesses by virtue of its position (i.e. height with respect to the surface of the earth) or configuration (whether it is stretched/compressed, pushed or pulled to one side) is called its potential energy.

Potential energy is the energy possessed (or stored) by a body due to its relative position or change in shape.

Factors Influencing Potential Energy

Potential energy depends upon the height of the object above the surface of the earth; greater the height, greater the potential energy.

Potential energy depends upon the change of configuration (stretching/compression, etc.,) of an object; greater the change in configuration, greater the potential energy; greater the weight of the object, greater the potential energy.

When a body possesses potential energy, it has to be changed into some other form of energy before it can be used.

For instance, a stationary rock on top of a mountain is not dangerous until its potential energy changes to kinetic energy, i.e., until it begins to roll down the mountain.


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