Lesson Notes By Weeks and Term v4 - JHS 2

Lesson Video

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Performance objectives

• Identify the main types of forces acting on structures.
• Perform simple experiments to demonstrate these forces.
• Observe and record the outcomes of the experiments.
• Apply your understanding to real-life structures.

Lesson summary

Time: [Enter Time] Overview and Learning Objectives

Lesson notes

This is the main content for the lesson. What are Structures and Forces? Structure: Anything that is built or constructed from different parts to support a load or span a distance. Examples: a building, a bridge, a chair, a table, a roof truss. Member: A single piece or component of a structure. Example: a leg of a chair, a pillar of a building, a beam in a roof. Force: A push or a pull on an object. Forces can cause an object to change its shape, size, or motion. In structures, we are mostly concerned with how forces change the shape of members. The Five Main Types of Forces on Structures

We will explore five key forces. For each force, we will look at its definition, a simple diagram, and a real-world example. Tension (A Pulling Force) Explanation: Tension is a force that pulls on a member, trying to stretch it or make it longer. Think of a tug-of-war game; the rope is in tension. Diagram: ``` (Arrows show pulling outwards) ``` Ghanaian Context: The long steel cables holding up the road on the Adomi Bridge are under tension. A clothesline with wet clothes hanging on it is also in tension. Compression (A Squeezing or Pushing Force) Explanation: Compression is a force that pushes or squeezes a member, trying to make it shorter or more compact. If the member is long and thin, compression can cause it to buckle (bend outwards). Diagram: ``` --->[ MEMBER ]<--- (Arrows show pushing inwards) ``` Ghanaian Context: The concrete pillars holding up the porch of a house are under compression. When you sit on a wooden stool, its legs are in compression. The pestle used for pounding fufu exerts a compression force on the fufu in the mortar. Shear (A Cutting or Sliding Force) Explanation: Shear forces act in opposite directions across a material, trying to make one part of the material slide over the other part. Diagram: ``` ↓ [ MEMBER ] ↑ ``` Ghanaian Context: A pair of scissors cutting paper uses shear force. The blades push on the paper in opposite directions. The bolts or rivets holding metal sheets together on a tro-tro are under shear force. Torsion (A Twisting Force) Explanation: Torsion is a force that twists a member. It happens when a turning force is applied to an object. Diagram: ``` ↻ [ MEMBER ] ↺ (Arrows show twisting in opposite directions) ``` Ghanaian Context: Wringing a wet cloth to squeeze out water is a perfect example of torsion. A carpenter using a screwdriver to drive a screw into wood applies a torsion force. Bending (A Curving Force) Explanation: Bending is a complex force that happens when a force is applied at an angle to a member, causing it to curve. Bending is actually a combination of tension and compression. The top surface of the bend is compressed, and the bottom surface is stretched (tension). Diagram: ``` ↓ (Load) [----MEMBER----] ▲ ▲ (Supports) ``` Ghanaian Context: A wooden plank placed across a small gutter to walk on experiences a bending force when someone stands on it. The branch of a mango tree bends when heavy mangoes grow on it.

Activity: Group Experiments on Forces (Core of the Lesson)

(Teacher's Note: Divide learners into groups of 4-5. Distribute the TLMs. Ask each group to perform the following experiments and write down their observations.)

Evaluation guide

• B8.4.1.1
• Demonstrate understanding
• of application of principles of
• forces acting on structures