Potential Energy

The term potential energy was introduced by the 19th-century Scottish engineer and physicist William Rankine. There are several types of potential energy, each associated with a distinct type of force. It is the energy by virtue of an object’s position relative to other objects.

Table of Content

What is Potential Energy?

As we know, an object can store energy as a result of its position. In the case of a bow and an arrow, when the bow is drawn, it stores some amount of energy, which is responsible for the kinetic energy it gains, when released. We can define potential energy as:

The energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors.

Similarly, in the case of a spring, when it is displaced from its equilibrium position, it gains some amount of energy which we observe in the form of stress we feel in our hand upon stretching it. We can define potential energy as a form of energy that results from the alteration of its position or state.

Potential Energy Formula

The formula for potential energy depends on the force acting on the two objects. For the gravitational force the formula is:

W = m×g×h = mgh
Where,
  • m is the mass in kilograms
  • g is the acceleration due to gravity
  • h is the height in meters

Unit:

Gravitational potential energy has the same units as kinetic energy: kg m2 / s2
Note: All energy has the same units – kg m2 / s2, and is measured using the unit Joule (J).

Learn the difference between kinetic energy and potential energy from the video below:

 

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What are the different types of potential energy?

Potential energy is one of the two main forms of energy, along with kinetic energy. There are two main types of potential energy and they are:

  • Gravitational Potential Energy
  • Elastic Potential Energy

Gravitational Potential Energy

The gravitational potential energy of an object is defined as the energy possessed by an object rose to a certain height against gravity. We shall formulate gravitational energy with the following example.

  • Consider an object of mass = m.
  • Placed at a height h from the ground, as shown in the figure.

Now, as we know, the force required to raise the object is equal to m×g of the object.

Gravitational Potential Energy

As the object is raised against the force of gravity, some amount of work (W) is done on it.

Work done on the object = force × displacement.

So,

W = m×g×h = mgh

Above is the potential energy formula.

As per the law of conservation of energy, since the work done on the object is equal to m×g×h, the energy gained by the object = m×g×h, which in this case is the potential energy E.

E of an object raised to a height h above the ground = m×g×h

Potential Energy Example

It is important to note that, the gravitational energy does not depend upon the distance travelled by the object, but the displacement i.e., the difference between the initial and the final height of the object. Hence, the path along which the object has reached the height is not taken into consideration. In the example shown above, the gravitational potential energy for both the blocks A and B will be the same.

Elastic Potential Energy

Elastic potential energy is the energy stored in objects that can be compressed or stretched such as rubber bands, trampoline and bungee cords. The more an object can stretch, the more elastic potential energy it has. Many objects are specifically designed to store elastic potential energy such as the following:

  • A twisted rubber band that powers a toy plane
  • An archer’s stretched bow
  • A bent diver’s board just before a diver dives in
  • Coil spring of a wind-up clock

An object that stores elastic potential energy will typically have a high elastic limit, however, all elastic objects have a threshold to the load they can sustain. When deformed beyond the elastic limit, the object will no longer return to its original shape.

Elastic potential energy can be calculated using the following formula:
\(U=\frac{1}{2}kx^2\)

Where,

  • U is the elastic potential energy
  • k is the spring force constant
  • x is the string stretch length in m

Potential Energy Examples

Following are a few potential energy examples:

Potential energy of stones on top of a cliff

Stones sitting on an edge of a cliff possess potential energy. If the stones fall the potential energy will be converted to kinetic energy.

Potential energy of tree branches

Tree branches high up the tree have potential energy because they can fall to the ground.

Potential energy of tree branches

The food that we eat is comprised of chemical potential energy. Our body digests this potential energy and provides the necessary energy for bodily functions.

Chemical potential energy of fircracker

The chemical potential energy of a firecracker is released when the fuse of the firecracker is lit.

Potential Energy Practice Question:

Q1: What will be the gravitational potential energy possessed by a ball of mass 1 kg when it is raised to a height of 6 m above the ground. (g = 9.8 m s–2)

Solution:
Here, the mass of the object (m) = 1 kg,
Displacement (height) (h) = 10 m,
Acceleration due to gravity (g) = 9.8 m s–2.
Hence, Potential energy (p) = m×g×h = 1 kg × 9.8 m s–2 × 10 m = 98 J.

Frequently Asked Questions on Potential Energy

Who coined the term potential energy?

The term potential energy was first used by a Scottish engineer and physicist named William Rankine during the 19th century. The concept of potential energy dates all the way back to Aristotle.

Name some objects that possess elastic potential energy.

Objects such as rubber bands, trampolines, and bungee cords all have elastic potential energy.

What are the factors that gravitational potential energy an object depends on?

The amount of gravitational potential energy an object has depends on its height above the ground and its mass. The heavier an object and the higher it is above the ground, the more gravitational potential energy it has.

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