Elastic Potential Energy (AQA GCSE Physics)

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Elastic Potential Energy

What is Elastic Potential Energy?

  • Energy in the elastic potential store of an object is defined as:

The energy stored in an elastic object when work is done on the object

  • This means that any object that can change shape by stretching, bending or compressing (eg. springs, rubber bands)
    • When a spring is stretched (or compressed), work is done on the spring which results in energy being transferred to the elastic potential store of the spring
    • When the spring is released, energy is transferred away from its elastic potential store

Load extension and force, downloadable AS & A Level Physics revision notes

How to determine the extension, e, of a stretched spring

How to Calculate Elastic Potential Energy

  • The amount of elastic potential energy stored in a stretched spring can be calculated using the equation:

Ee = ½ × k × e2

  • Where:
    • Ee = elastic potential energy in joules (J)
    • k = spring constant in newtons per metre (N/m)
    • e = extension in metres (m)

  • The above elastic potential energy equation assumes that the spring has not been stretched beyond its limit of proportionality

Elastic-limit, IGCSE & GCSE Physics revision notes

The spring on the right has been stretched beyond the limit of proportionality

Worked example

A mass is attached to the bottom of a hanging spring with a spring constant of 250 N/m. It stretches from 10.0 cm to 11.4 cm.

Calculate the elastic energy stored by the stretched spring.

 

Step 1: Determine the extension of the spring

Extension Worked Example, downloadable IGCSE & GCSE Physics revision notes

 

Step 2: List the known quantities

    • Spring constant, k = 250 N/m
    • Extension, e = 1.4 cm = 0.014 m

Step 3: Write out the elastic potential energy equation

Ee = ½ ke2

Step 4: Calculate the elastic potential energy

Ee = ½ × 250 × (0.014)2

Ee= 0.0245 J

Step 5: Round the answer to 2 significant figures

Ee = 0.025 J

Exam Tip

Look out for units! If the question gives you units of cm for the length you MUST convert this into metres for the calculation to be correct.

Leander, Physics

Teacher tip

Leander

Physics

In my experience of teaching this topic at GCSE, it helps to draw on the students' Key Stage 3 knowledge of forces. To change the shape of an object, two contact forces must be acting on the object in different directions. In this case, the spring is attached to the arm of the clamp providing a contact force, and the mass is attached to the spring providing a contact force. These forces pull the spring in opposite directions and this is the reason that the spring stretches. The forces and energy topics are linked by the concept of work done which is a force acting over a distance, and also the energy transferred. Making links between concepts is an important way to fast-track your understanding. I recommend you create a mind map as you revise the course as this is a great visual way to establish linked concepts.

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Leander

Author: Leander

Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.