Lesson Notes By Weeks and Term v4 - JHS 1

Lesson Video

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Performance objectives

• Define resistant materials and their importance.
• Identify types of resistant materials used in Ghana.
• Describe the properties that make materials resistant.
• Give examples of how resistant materials are used in everyday life.

Lesson summary

This lesson introduces learners to the fascinating world of resistant materials. These are the strong, tough materials we use every day to build our homes, make our furniture, cook our food, and create tools. From the wooden desk you are sitting at, to the metal roofing sheets on our school, and the plastic bowl you used this morning, resistant materials are the backbone of our physical world. Understanding them is the first step to becoming a great designer, engineer, or artisan. We will explore what makes these materials "resistant" and learn to identify them in our own Ghanaian communities.

Lesson notes

This section breaks down everything you need to know about resistant materials. A. What is a Resistant Material?

A resistant material is a type of material that can withstand forces and wear without easily breaking, bending, or getting damaged. Think of it as a very strong and tough material. It "resists" or "fights back" against being changed.

The forces it can resist include: Compression: A squashing or pressing force (e.g., the legs of a chair resisting your weight). Tension: A pulling or stretching force (e.g., a rope in a tug-of-war). Bending: A force that tries to curve the material. Abrasion: A scratching or rubbing force (e.g., sandpaper on wood). Corrosion/Rotting: Damage from chemicals, water, or air (e.g., rust on iron). B. Main Categories of Resistant Materials

For our level, we will focus on the three most common categories: Woods, Metals, and Plastics. WOOD Source: Wood is a natural material that comes from trees. Types: Hardwoods: Come from broad-leafed, deciduous trees (trees that lose their leaves in the dry season). They are generally stronger, denser, and more expensive. *Ghanaian Examples:* Odum, Mahogany, Sapele. These are excellent for making high-quality furniture and building frames because they are very durable. Softwoods: Come from coniferous trees (trees with needles and cones). They grow faster, are less dense, and cheaper. *Ghanaian Examples:* Wawa, Pine, Cedar. Wawa is very common in Ghana and is used for making things like ceiling boards, plywood, and carving stools. Properties of Wood: Strong and durable, especially hardwoods. Good insulator: It does not conduct heat or electricity well. This is why the handle of a cooking pot might be wooden. Aesthetically pleasing: It has a natural beauty (grain patterns). Workable: It can be easily cut, carved, and shaped. Disadvantage: Can rot or be eaten by insects if not treated with chemicals or varnish. METALS Source: Metals are usually found in the ground as ores, which are then processed to get the pure metal. Types: Ferrous Metals: These metals contain iron. Their main characteristic is that they are magnetic and they rust (corrode) if left exposed to moisture and air. *Examples:* Steel (iron + carbon), Cast Iron. Iron rods used in building pillars are made of steel. Non-Ferrous Metals: These metals do not contain iron. They do not rust and are not magnetic. *Examples:* Aluminium (used for cooking pots, roofing sheets), Copper (used for electrical wires), Zinc (used to coat steel to prevent rusting - this is called galvanizing). Properties of Metals: Very strong and tough. Good conductors of heat and electricity. This is why they are used for pots and wires. Ductile (can be drawn into wires) and Malleable (can be beaten into thin sheets). High melting point: Can withstand high temperatures. Disadvantage: Ferrous metals rust; many metals are heavy and expensive. PLASTICS Source: Most plastics are synthetic (man-made) materials derived from crude oil. Types: Thermoplastics: These plastics can be softened by heating, remoulded, and then set again when they cool. They can be recycled easily. *Examples:* PET (used for water/drink bottles), HDPE (used for "Kuffour" gallons and buckets), PVC (used for pipes and electrical insulation). Thermosetting Plastics: These plastics are set permanently during manufacturing. They cannot be remelted or reshaped. *Examples:* Bakelite (used for electrical sockets and old telephone casings), Melamine (used for durable plates and bowls). Properties of Plastics: Lightweight. Waterproof and corrosion-resistant. Good electrical and heat insulators. Can be easily moulded into complex shapes. Can be produced in many colours. Disadvantage: Most are not biodegradable (they don't rot), which causes environmental pollution. Some can become brittle in the sun. C. Key Properties Explained with Examples