Lesson Notes By Weeks and Term v4 - SHS 2
MATTER
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MATTER
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Subject: Physics
Class: SHS 2
Term: 1st Term
Week: 5
Grade code: 2.1.2.LI.3
Strand code: 1
Sub-strand code: 2
Content standard code: 2.1.2.CS.1
Indicator code: 2.1.2.LI.3
Theme: MECHANICS AND MATTER
Subtheme: MATTER
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This lesson explores the concept of energy stored in materials that can be stretched or compressed, a property known as elasticity. In our daily lives in Ghana, we see this principle everywhere ā from the simple rubber band used to tie our *gari* and sugar, to the springs in a *tro-tro's* suspension that absorb the shock from potholes, and even the "chale-wote" (catapult) used in play. Understanding how to calculate this stored energy, known as Elastic Potential Energy, is fundamental to engineering, design, and understanding the world around us. Today, we will learn how the work we do to stretch a material is stored as energy and how to calculate it using graphs and formulas.
This lesson builds on our previous knowledge of Hooke's Law. Let's briefly recap before we move forward. Recap: Hooke's Law Hooke's Law states that for an elastic material, the force (F) applied is directly proportional to the extension (e) it produces, as long as the elastic limit is not exceeded. Formula: F = ke Where: F is the applied force (or load) in Newtons (N). e is the extension (the change in length) in meters (m). k is the spring constant (or force constant), a measure of the stiffness of the material, in Newtons per meter (N/m). Concept 1: Work Done and Stored Energy When you stretch a rubber band, you are applying a force over a distance. This means you are doing work on the rubber band. Where does this work go? It is stored within the stretched rubber band as a form of potential energy. We call this Elastic Potential Energy (Eā).
> Definition: Elastic Potential Energy is the energy stored in an elastic object as a result of its deformation (stretching or compressing).
If you release the stretched rubber band, this stored energy is converted into kinetic energy, which is why it can be used to launch a small stone from a catapult. The amount of energy stored is exactly equal to the work done to stretch it. Concept 2: The Load-Extension Graph and Energy The NaCCA exemplar guides us to use a graph to understand this concept. Let's consider a typical load-extension graph for a material obeying Hooke's Law. The vertical axis (y-axis) represents the Load or Force (F). The horizontal axis (x-axis) represents the Extension (e).
The graph is a straight line passing through the origin, up to the elastic limit.