Lesson Notes By Weeks and Term v4 - SHS 2

Lesson Video

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Performance objectives

• Define elasticity and a load-extension graph.
• Explain how energy is stored in a deformed material.
• Calculate the energy stored using the area under the load-extension graph.
• Relate these principles to real-life situations in Ghana.

Lesson summary

In our daily lives in Ghana, we see and use elastic materials everywhere. When you stretch the rubber band used to tie a ball of kenkey, pull back a catapult ("chale-wote") to aim at a target, or watch a 'trotro' bounce on its suspension after hitting a pothole, you are witnessing the storage and release of energy. This stored energy is called Elastic Potential Energy. Understanding how to calculate this energy is crucial for engineers designing safer cars, for athletes improving their performance in sports like pole vaulting, and for appreciating the simple physics in our everyday tools.

Lesson notes

This topic builds directly on our previous knowledge of Hooke's Law. Let's start with a quick recap. Recap: Hooke's Law Hooke's Law states that, provided the elastic limit is not exceeded, the extension `(e)` of an elastic material is directly proportional to the applied force or load `(F)`. Mathematically: `F ∝ e` This gives us the famous equation: `F = ke` `F` is the applied force (in Newtons, N). `e` is the extension or compression (in metres, m). `k` is the spring constant or force constant (in Newtons per metre, N/m). It is a measure of the stiffness of the material. Work Done and Stored Energy To stretch a spring or a rubber band, you must pull on it. Pulling on it means you are applying a force over a distance. In physics, Work Done = Force × Distance.

When you stretch an elastic material, you are doing work on it. This work is not lost; it is transferred to the material and stored as Elastic Potential Energy (EPE). When the material is released, this stored energy can be converted into other forms, like the kinetic energy of a stone fired from a catapult.

Key Idea: *Work Done in stretching the material = Energy Stored in the material*

However, there's a small complication. The force required to stretch the spring is not constant. It starts at zero (when there's no extension) and increases linearly to a final value `F` (as described by Hooke's Law).

Evaluation guide

• Calculate the energy stored in an elastic material.
• Project – based learning : Let learners calculate the area under the load -extension graph and guide
• learners to deduce the energy store.
• conceptual