7.4.2 Potential Energy

Example 1

Suppose we stretch a rubber band. Does it have any energy?

GIF Watch: what is Potential Energy

Yes. When we release it, it applies a force on the object in contact with it (like a stack of coins) and makes it move.
It gives kinetic energy to that object.
So it has energy.
We say that this energy is as a result of deformation of the rubber band (changing form of the rubber band).

Example 2

Suppose we lift a heavy object. Does it have any energy?

GIF Watch: what is Potential Energy

Yes. When we release it, it falls down and gains speed.
If it falls on something (like sand), it can create a depression — it does work.
So it has energy.
We say that this energy is as a result of its position (its height above the ground).

What is Potential Energy?

The energy stored by an object as a result of its deformation, or in a system of objects due to their relative positions, is called potential energy.
In easy language — energy stored due to shape or position.
The unit of potential energy is the joule (J) — same as work and kinetic energy.

How is energy stored by changing shape (deformation)?

When we stretch or bend an object, we do work on it.
This work gets stored in the object as potential energy.
When the object is released, it comes back to its original shape and gives this stored energy to whatever is in contact with it.

Example	What we do	What happens on release
Slingshot (gulel)	We stretch the elastic band	The object in contact shoots forward
Bow and arrow	Archer pulls the string, bow arms bend	Bow returns to original shape, arrow flies off
Spring	We compress or stretch it	Spring pushes the object in contact and sets it in motion
Rubber band (Activity 6.1 of Chapter 6)	We stretch it against a stack of coins	Released band makes the coins move

In each case
- The stretched band or bent bow applies a force on the object in contact.
- This sets the object in motion — gives it kinetic energy.
- This kinetic energy came from the stored energy of the band or the bow.
- The work done to deform them was stored in them as potential energy.

How is energy stored by changing position (arrangement)?

Energy can be stored not only by deforming an object, but also by changing the arrangement of objects in a system.
Two magnets
- GIF Watch: what is Potential Energy
- Unlike poles of two magnets attract each other.
- To separate them, we have to apply a force — we do work.
- When released, they rush towards each other and gain kinetic energy.
- In fact, a small pea kept between two strong magnets can even be crushed by their kinetic energy.
- So the separated magnets store energy due to their relative positions.
Electric charges
- GIF Watch: what is Potential Energy
- A system of electric charges separated by a distance also stores energy.
- This stored energy can do work when they are released.
Ball and Earth
- GIF Watch: what is Potential Energy
- A ball and the Earth attract each other (gravitational force).
- To lift the ball to a height, we do work against the gravitational force.
- Once lifted and released, the ball and the Earth rush towards each other — the ball attains kinetic energy.
- So the ball-Earth system, when separated, stores energy due to their relative positions.
More generally — whenever a system of objects interacts through forces (gravitational, electric or magnetic), the system can store energy due to the relative positions of the objects.

📝 Important points — 7.4.2 Potential Energy

Point	Detail
Potential energy	Energy stored due to deformation or relative positions
Two ways to store	Change shape (spring, bow) or change position (separate magnets, lift a ball)
Unit	joule (J)

🚀 Ready to Go Beyond

You need to apply an external force to overcome the internal forces in the spring to deform it. Once you remove this external force, the internal forces undo the deformation, and in the process, it can carry out work. Thus, internal forces allow energy to be stored in a deformed object.

💡 Worth remembering

Kinetic energy needs motion. Potential energy needs NO motion — a still stretched spring, a still ball at a height, both have energy.
Deformation stores energy. Separation (against an attracting force) also stores energy.

✅ Quick self-check

A stretched rubber band is held still. Does it have energy? Which type?
View Answer Hide Answer
- Yes — it is deformed, so the work done to stretch it is stored in it.
- It has potential energy (due to its changed shape).
Two magnets with unlike poles facing each other are pulled apart and held. Do they store energy?
View Answer Hide Answer
- Yes — work was done against their attraction to separate them.
- The system stores potential energy due to the relative positions of the magnets.

Term	Meaning	Unit
Potential energy (U)	Energy stored due to deformation or position	joule (J)

Class 6