Lesson Notes By Weeks and Term v4 - SHS 1

Lesson Video

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Performance objectives

• Identify and describe the properties of different solids.
• Explain how the properties of solids influence their uses.
• Analyze real-world scenarios to choose suitable materials.
• Apply knowledge of material properties to solve practical problems.

Lesson summary

Welcome, students! Look around you. The chair you are sitting on, the pen in your hand, the concrete walls of this classroom, and the mobile phone in your pocket are all made of solid materials. But have you ever wondered *why* a particular material was chosen for a specific job? Why is the handle of a cooking pot made of wood or plastic and not metal? Why are electrical wires made from copper and not from rubber? In Ghana, from the strong Odum wood used for furniture in Akyem to the clay used for pots in the Volta Region, our lives are shaped by the clever use of solid materials.

Lesson notes

The usefulness of a solid material depends on its unique characteristics, which we call properties. Let's explore the most important ones. A. Mechanical Properties (How a solid responds to forces) Hardness and Strength Definition: Hardness is the ability of a material to resist scratching, abrasion, or indentation. Strength is the ability of a material to withstand a force without breaking or deforming permanently. A very hard material is not always strong (e.g., glass is hard but breaks easily). Why it Matters: We need strong materials for building structures that can support weight and hard materials for surfaces that must resist wear and tear. Ghanaian Example: Concrete Blocks: Used to build our homes and schools. They have high compressive strength, meaning they can support the immense weight of a roof without being crushed. Diamond: Used on the cutting edges of tools for drilling or cutting hard rock in our mining communities (e.g., Obuasi, Tarkwa). Diamond is the hardest known natural material. Malleability and Ductility Definition: Malleability is the ability of a solid to be hammered or pressed into a thin sheet without breaking. Ductility is the ability of a solid to be drawn into a thin wire. Most metals are both malleable and ductile. Why it Matters: These properties allow us to shape metals into useful objects. Ghanaian Example: Goldsmiths: A goldsmith in Kejetia or Accra can take a small piece of gold and hammer it into beautiful, thin earrings or intricate necklaces. This is possible because gold is highly malleable. Aluminium Roofing Sheets: Large rolls of aluminium are pressed and shaped into the corrugated sheets we use for roofing all over Ghana. This is an application of malleability. Copper Wires: The copper used for electrical wiring is stretched into long, thin wires because it is very ductile. Elasticity and Plasticity Definition: Elasticity is the ability of a material to return to its original shape and size after a deforming force is removed. Plasticity is the opposite; the material remains permanently deformed after the force is removed. Why it Matters: Elasticity is crucial for things that need to bend and return to shape, while plasticity is useful for things we want to shape permanently. Ghanaian Example: Car Tyres/Rubber Bands: The rubber used in vehicle tyres has high elasticity. It deforms when it hits a pothole on our roads but immediately returns to its original shape, providing a smoother ride. Clay for Pottery: A potter in Vume (Volta Region) uses wet clay, which has high plasticity. They can mould it into an 'asanka' or a water pot, and it will hold that new shape permanently after drying and firing. Brittleness Definition: Brittleness is the tendency of a material to break or shatter suddenly with little or no plastic deformation when subjected to a force. Why it Matters: We must be careful when using brittle materials for applications where they might experience sudden impacts. Ghanaian Example: Glass Louvres: The glass blades used in our windows are brittle. They are hard and transparent, but a strong impact from a stone or football will cause them to shatter. Earthenware (Clay) Pots: A traditional clay pot will shatter if dropped, demonstrating its brittle nature. B. Physical Properties Thermal and Electrical Conductivity Definition: Conductivity is the ability of a material to allow heat (thermal) or electricity (electrical) to pass through it. Materials that do not allow this are called insulators. Why it Matters: We use conductors when we want to transfer heat or electricity and insulators when we want to prevent their transfer for safety or efficiency. Ghanaian Example: Conductors: The base of an aluminium cooking pot (dadesen) is a good thermal conductor, allowing heat from the coal pot or gas stove to quickly reach the food. Copper is used for electrical wires because it is an excellent electrical conductor. Insulators: The handle of that same cooking pot is often made of wood or plastic. These are thermal insulators, preventing heat from travelling to your hand and burning you. The plastic coating around electrical wires is an electrical insulator, preventing electric shock. Density Definition: Density is the mass of a substance per unit volume (Density = Mass/Volume). In simple terms, it's how "heavy" a material is for its size. Why it Matters: We choose low-density materials for things that need to be light (like aeroplanes) and high-density materials for things that need to be heavy (like anchors). Ghanaian Example: Wawa Wood: This is a low-density Ghanaian wood. It is often used for ceiling boards or carving because it is light and easy to work with. Iron Rods: Used to reinforce concrete in buildings. Iron has a high density, which contributes to the overall strength and stability of the structure.

Guided Practice (With Solutions)

Here are some problems to solve together. Think through the steps logically.

Question 1: The Cooking Pot Problem

Evaluation guide

• Apply the properties of solids to everyday use .
• Learners research how the properties of different solids relate to their uses in life. Provide
• opportunities for students to evaluate various real -world scenarios and make decisions based
• conceptual