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# Elastic Potential Energy - JEE Important Topic

## What is Potential Energy?

Last updated date: 30th Mar 2023
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Potential energy is the energy that an object possesses due to its pressure, electric charge, or relatively stationary position in space. It is the body's innate energy in relation to its still location in relation to other objects. One of the two primary forms of energy is potential energy, the other being kinetic energy. Elastic potential energy and gravitational potential energy are the two different types of potential energy.

## What is Elastic Potential Energy?

The energy that is stored when a force is used to deform an elastic object is known as elastic potential energy. Until the force is released and the object springs back to its original shape, doing labour in the process, the energy is retained. The object may be compressed, stretched, or twisted during the deformation.

## Elastic Energy Examples

Numerous items are made to hold elastic potential energy, such as:

• The coil spring of a wind-up clock

• An archer's stretched bow

• A bent diving board, just before a diver’s jump

• The twisted rubber band that powers a toy airplane

• A bouncy ball, compressed at the moment, bounces off a brick wall.

## Definition of Stress, Strain, and Young's Modulus

Stress: The definition of stress is force per unit area, where F is the applied force, and A is the cross-sectional area.

• Tensile Stress: Stress that has a propensity to extend or stretch the material - behaves normally in the stressed area.

• Compressive Stress: Stress that has a propensity to shorten or compress the material - behaves normally in the stressed area.

• Shearing Stress: Stress that has a propensity to shear the material - compressive or tensile stress acts perpendicular to the strained area at right angles.

Strain: Strain is defined as the deformation of a solid due to stress.

• Normal strain: lengthening or shortening of a line segment.

• Shear strain: Angle difference between two lines that were once perpendicular.

Young's Modulus: Over a range of loads, most metals deform in proportion to the applied force. According to Hooke's Law, strain is proportional to deformation, and stress is proportional to load.

## Elastic Potential Energy in a Stretched Wire Formula

A specific amount of labour must be done against restoring force to stretch a wire. The potential energy (U) of the stretched wire is where this work is stored.

Consider a wire that is being bent by a deforming force of length "L" and cross-section area "A". The subsequent modest task performed by "dw" to be extended by "dl" is given by:

$dW=F~dl$                                                    ----(1)

Thus, by integrating dw between the limits of 0 and 'L', the total work 'W' required to extend the wire by length 'l' is determined.

Therefore,

$W=\int dw$

$W=\int_{0}^{l}F~dl$                                       ---(2)

Here, ‘F’ is elongation-dependent. Therefore, the definition of Young's Modulus (Y) when the elongation is ‘l’ yields

$Y=\dfrac{stress}{strain}=\dfrac{\dfrac{F}{A}}{\dfrac{l}{L}}$

$\therefore F=\dfrac{YAl}{L}$                            ----(3)

Using this in equation (2) and integrating, we get

$dW=W=\int_{0}^{l}{\dfrac{YAl}{L}}dl$

$W=\dfrac{YA}{L}\left[ \dfrac{l}{2} \right]_{0}^{l}$

$W=\dfrac{YA}{L}\left[ \dfrac{{{l}^{2}}-{{0}^{2}}}{2} \right]$

$=\dfrac{1}{2}\dfrac{YAl}{L}{{l}^{2}}$

$\therefore W=\dfrac{1}{2}F\times l$

This work is equivalent to the stored potential energy (U).

Energy stored (U) = work done (w)

$U=\dfrac{1}{2}force\times elongation$

## Elastic Potential Energy Formula in terms of Stress and Strain

The elastic potential energy of the stretched wire is the amount of energy it can hold relative to its volume.

$U=\dfrac{energy~stored}{volume}$

$=\dfrac{YF\times l}{A\times L}$

$=\dfrac{1}{2}\dfrac{F}{A}\times \dfrac{l}{L}$

$=\dfrac{1}{2}stress\times strain$

## Elastic After Effect

We are aware that when the deforming forces are removed from elastic bodies, they return to their original shape. The original configurations of some elastic bodies can be recovered right away, while for others, it takes some time. Elastic after effect is the transient delay experienced by an elastic body in returning to its initial shape following the removal of a deforming force.

## Elastic Fatigue

Elasticity is lost when a body is repeatedly deformed and released. Elastic fatigue is the term for this. After repeatedly deforming, an iron nail may break due to elastic fatigue.

## Elastic Hysteresis

Elastic hysteresis is the phenomenon where the strain produced in elastic lags behind the tension to which it is subjected as a result of elastic after-effect. The strain created when a body is subjected to the road cycle of growing and reducing stress is greater when the body is empty than when it is loaded.

## Conclusion

The potential energy that is held when an elastic item is stretched or compressed by an external force, such as the stretching of a spring, is known as elastic potential energy. It is equivalent to the work required to stretch the spring, which is dependent on both the length of the stretch and the spring constant k.

The elastic limit of an object intended to store elastic potential energy will normally be high. Still, the maximum load an elastic object can support is a property shared by all elastic objects. The elastic limit is the point at which an object can be deformed without losing its original shape.

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## FAQs on Elastic Potential Energy - JEE Important Topic

1. What are real elastic materials?

Rubber bands and flexible plastics are examples of elastic materials that can act as springs but they frequently exhibit hysteresis, which causes the force vs. extension curve to take a different route while the material is deformed than when it is relaxing back to its equilibrium position.

Thankfully, the fundamental method of using the definition of work that we applied for a perfect spring also applies to elastic materials in general. No matter how the curve is shaped, the elastic potential energy can always be calculated from the area under the force vs. extension curve.

2. List the uses of elastic energy.

In many mechanical systems, such as the shock absorbers found in cars, a spring is utilized to store elastic potential energy. Since the spring may stay in either it's compressed or stretched form for extended periods without losing energy, elastic energy can be employed in various ways.

Elastic energy is used to stretch in trampolines, rubber bands, balloons, and bungee cords. Stretchy objects like balls, a bow and arrow, and coiling springs utilize elastic energy. Elastic energy is used in slingshots and catapults, among other things.