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Lesson 02

Hooke's Law

Use load-extension data, Hooke's law, and spring constant ideas to describe elastic behaviour.

Objectives

Lesson outcomes

  • Describe how forces can change the size and shape of an object.
  • Sketch, plot, and interpret a load-extension graph for an elastic spring.
  • Use the equation F = kx and define the spring constant as force per unit extension.
  • Identify and explain the limit of proportionality on a load-extension graph.
Syllabus

CIE 0625 syllabus points

4 linked

Definitions

Required definitions

  • Hooke's law

    extension is proportional to the force applied, as long as the limit of proportionality has not been exceeded.

  • Spring constant

    force per unit extension.

  • Limit of proportionality

    the point after which Hooke's law is no longer obeyed.

  • Extension

    the new length minus the original length.

Lesson Notes

Student guidance and lesson notes

Overview

This lesson should tie together practical evidence, graphs, and the model of elastic behaviour.

What You Need to Know

  • Start with the idea that forces can stretch, compress, or deform an object, then narrow the focus to elastic behaviour in springs.
  • Use a spring-loading practical or clear data set to build a load-extension graph from measured results.
  • Keep the straight-line region central so you can see when extension is proportional to force.
  • Use the spring constant definition with F = kx in simple calculations.
  • Identify the limit of proportionality as the point where the graph stops being a straight line through the origin.

How to Work Through It

  1. Start with a short retrieval prompt on force and extension from everyday examples such as springs or elastic bands.
  2. Demonstrate or analyse the spring experiment and build the load-extension graph together.
  3. Use the graph to identify proportional behaviour, the spring constant, and the limit of proportionality.
  4. Finish with short calculation and graph-interpretation questions.

Check Your Understanding

  • Check whether you can decide whether a section of graph shows proportional behaviour and explain why.
  • Try one hinge question where you identify the spring constant from a graph or a data table.
  • Try one graph and check whether you can mark the limit of proportionality.

Common Mistakes

  • Assuming any stretched spring still obeys Hooke’s law. Keep the straight-line region and the limit of proportionality distinct.
  • Some confuse extension with total length. Keep both measurements visible in the worked method.
  • Unit conversion can weaken spring-constant calculations, especially when extension is given in centimetres instead of metres.

Next Steps

  • Use the past-paper question to reinforce graph reading and spring-constant calculations.
  • Carry forward the idea of resultant force and change in motion into Newton’s laws.
Lesson Resources

Materials for this lesson

Use these videos, slide decks, documents, or links to work through the lesson.