Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Define stress, strain, and loading.
• Explain the relationship between stress and strain.
• Calculate stress and strain using given data.
• Understand the role of a strain gauge.

Lesson summary

This lesson explores how engineering materials behave when forces are applied to them. In Ghana, from the construction of the Adomi Bridge and the new Tema Interchange to the fabrication of simple burglar-proof doors by a local welder, understanding how materials respond to forces is crucial for safety, durability, and cost-effectiveness. When we build, design, or manufacture anything, we apply forces (loads) to materials. This lesson will introduce the fundamental concepts of stress (the internal force a material feels) and strain (how much the material deforms).

Lesson notes

This section breaks down the core ideas of how materials react to forces. a) Loading

A load is simply an external force or set of forces acting on an object or a structure. In manufacturing and engineering, we must consider the types of loads a product will experience.

Types of Loading: Tensile Load (Tension): A pulling force that tends to stretch or elongate a material. *Example:* The steel cables holding up the Adomi Bridge are in tension. A rope in a tug-of-war is under tension. Compressive Load (Compression): A pushing or squeezing force that tends to shorten or compress a material. *Example:* The concrete pillars holding up a school building are in compression. The legs of your chair are under a compressive load from your weight. Shear Load: A force that acts parallel to a surface, causing one part of the material to slide over another part. *Example:* The force on a rivet or bolt holding two metal plates together is a shear force. Cutting paper with scissors involves applying shear loads.

 b) Stress (σ)

Evaluation guide

• Outline the effect of loading, stress and strain on materials .
• Experi
• ential Learning: Learners measure the strain of materials in the laboratory using the strain
• gauge and determine the stress of the materials according to the applied strain. Display lab work for others to critique .