potential energy| formula for potential energy | examples of potential energy

Описание: Suppose a brick is lying on the ground.
It has no energy so it cannot do any work.
Let us lift this brick to the roof of a house
Now, some work has been done in lifting this brick against the force of gravity.
This work gets stored up in the brick in the form of potential energy.
Thus, the energy of a brick lying on the roof of a house is due to its higher position with respect to the ground.
And if this brick falls from the roof-top, it can do some (undesirable) work in breaking the window-panes or somebody’s head !
The energy of brick lying on the roof-top is known as gravitational potential energy because it has been acquired by doing work against gravity.

Another type of potential energy is elastic potential energy, which is due to a change in the shape of the body.
The change in shape of a body can be brought about by compressing, stretching, bending or twisting.
Some work has to be done to change the shape of a body (temporarily).
This work gets stored in the deformed body in the form of elastic potential energy.
When this deformed body is released, it comes back to its original shape and size and the potential energy is given out in some other form.
For example, a wound up circular spring possesses elastic potential energy which drives a wound-up toy (such as a toy car) .
the normal shape of the circular spring used in winding toys.
When we wind-up the spring of a toy-car by using a winding key, then some work is done by us due to which the spring gets coiled more tightly

The work done in winding the spring gets stored up in the tightly coiled-up spring (or wound-up spring) in the form of elastic potential energy.
When the wound-up spring is slowly released, its potential energy is gradually converted into kinetic energy which turns the wheels of the toy car and makes it run.
Thus, a wound-up spring can do work in returning to its original shape during unwinding.
The potential energy of a wound-up spring is not due to its position above the ground, it is due to the change in its shape

When we do work in stretching the rubber strings of a catapult (gulel), then the work done by us gets stored in the stretched rubber strings in the form of elastic potential energy
The stretched strings of a catapult possess potential energy due to a change in their shape (because they become long and thin).
This energy of the stretched strings of the catapult can be used to throw away a piece of stone with a high speed
We can now say that : The energy of a body due to its position or change in shape is known as potential energy.

Actually, the energy of a body due to its position above the ground is called gravitational potential energy and the energy of a body due to a change in its shape and size is called elastic potential energy.
Elastic potential energy is associated with the state of ‘compression’ or ‘extension’ of an object.
For example, the energy possessed by a ‘compressed spring’ or an ‘extended spring’ (stretched spring) is the elastic potential energy.


A bent bow has also potential energy stored in it.
The potential energy stored in the bent bow (due to change in its shape) is used in the form of kinetic energy in throwing off an arrow.
It is obvious that a body may possess energy even when it is not in motion.
And this energy is called potential energy.
A body can have both potential energy as well as kinetic energy at the same time.
The sum of the potential and kinetic energies of a body is called its mechanical energy.
A flying bird, a flying aeroplane, and a man climbing a hill, all have kinetic energy as well as potential energy.
A stationary stone lying at the top of a hill has only potential energy.
When this stone starts rolling downwards, it has both kinetic and potential energy.
And when the stone reaches the bottom of the hill, it has only kinetic energy.
The potential energy of a body is due to its higher position above the earth and it is equal to the work done on the body, against gravity, in moving the body to that position.
So, to find out the potential energy of a body lying at a certain height, all that we have to do is to find out the work done in taking the body to that height.
Suppose a body of mass m is raised to a height h above the surface of the earth
The force acting on the body is the gravitational pull of the earth m×g which acts in the downward direction.
To lift the body above the surface of the earth, we have to do work against this force of gravity.
Now, Work done = Force × Distance
So, W =m × g × h
This work gets stored up in the body as potential energy.
Thus, Potential energy = m × g × h
where m =mass of the body
g =acceleration due to gravity
h =height of the body above a reference point, say the surface of earth