Lesson Notes By Weeks and Term v4 - SHS 2
MATTER
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
MATTER
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Physics
Class: SHS 2
Term: 1st Term
Week: 5
Grade code: 2.1.2.LI.2
Strand code: 1
Sub-strand code: 2
Content standard code: 2.1.2.CS.1
Indicator code: 2.1.2.LI.2
Theme: MECHANICS AND MATTER
Subtheme: MATTER
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
Welcome, future engineers, scientists, and problem-solvers! Today, we are exploring a fundamental property of matter called elasticity. Have you ever stretched a rubber band to shoot a piece of paper? Or watched the suspension of a "tro-tro" or an "okada" move up and down on a bumpy road? Or even used a spring balance at the market to buy yams or fish? All these everyday experiences are governed by the principles we will learn today, particularly a rule discovered by a scientist named Robert Hooke. Understanding this topic is crucial because it helps us design everything from safe buildings and bridges to comfortable furniture and precise measuring instruments.
This section breaks down the core ideas you need to master. a) Elasticity and Plasticity Elasticity: This is the ability of a material to return to its original shape and size after a deforming force (a stretch or a squeeze) is removed. Think of a spring or a rubber band. Elastic Material: A material that shows elasticity. Examples: steel, rubber, copper. Plasticity (or Plastic Deformation): This is the opposite. If you apply a force and the material *does not* return to its original shape, it has undergone plastic deformation. It is permanently deformed. Think of stretching "chewing gum" or soft clay (putty). b) Hooke's Law
In the 17th century, a brilliant scientist named Robert Hooke studied how elastic materials behave. He discovered a very important relationship. Statement of the Law: Hooke's Law states that, provided the elastic limit is not exceeded, the extension of an elastic material is directly proportional to the applied force (or load). What does "directly proportional" mean? It means if you double the force, you double the extension. If you triple the force, you triple the extension. They change together in a constant ratio. Mathematical Formula: We can write this relationship as: `F ∝ e` Where: `F` is the applied force (also called Load), measured in Newtons (N). `e` is the extension (how much the material stretched), measured in metres (m).
To turn a proportionality into an equation, we introduce a constant of proportionality, `k`.
F = ke k is the spring constant (also called force constant or stiffness of the spring). The unit of `k` is Newtons per metre (N/m or Nm⁻¹). `k` tells us how stiff the material is. A high value of `k` means the spring is very stiff and hard to stretch. A low value of `k` means the spring is "soft" and easy to stretch.