Lesson Notes By Weeks and Term v4 - SHS 1
SCIENCE AND MATERIALS IN NATURE
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SCIENCE AND MATERIALS IN NATURE
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Subject: General Science
Class: SHS 1
Term: 1st Term
Week: 2
Grade code: 1.1.1.LI.2
Strand code: 1
Sub-strand code: 1
Content standard code: 1.1.1.CS.2
Indicator code: 1.1.1.LI.2
Theme: EXPLORING MATERIALS
Subtheme: SCIENCE AND MATERIALS IN NATURE
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Welcome, future scientists and engineers! Look around you—the chair you are sitting on, the pen in your hand, the concrete walls of this classroom, and the roofing sheets on top. Have you ever wondered why a chair is made of wood or plastic and not glass? Or why our electrical wires are made of copper and not rubber? The answer lies in the properties of these materials. In Ghana, from the blacksmith in our local community shaping a hoe, to the engineer choosing iron rods for a new high-rise building in Accra, to the market woman choosing an aluminum pot over a clay pot for her waakye, people are constantly making choices based on the properties of solids.
The usefulness of a solid material depends on its unique set of characteristics, which we call properties. Let's break down the most important ones. A. Mechanical Properties (How a material behaves under force)
These properties describe how a material responds when you push, pull, twist, or bend it. Strength: This is the ability of a material to resist breaking under a load or force. Tensile Strength: Ability to resist being pulled apart (e.g., a rope in a tug-of-war). Compressive Strength: Ability to resist being squeezed or crushed (e.g., a concrete pillar holding up a building). Ghanaian Example: Iron rods are used with concrete to build houses and bridges because they have very high tensile strength, while concrete has high compressive strength. Together, they form a very strong material called reinforced concrete. Hardness: This is the ability of a material to resist scratching, cutting, or indentation (denting). A harder material can scratch a softer one. Example: Diamond is the hardest known natural substance. It is used in tools for cutting glass or drilling through rock. Ghanaian Example: The blade of a cutlass (machete) must be made of hard steel so it can keep a sharp edge and cut through wood without becoming blunt easily. Granite, a very hard rock, is used for kitchen countertops because it doesn't scratch easily. Malleability: The ability of a solid to be hammered or pressed into a thin sheet without breaking. Example: Gold is very malleable. A small piece can be hammered into a very large, thin sheet (gold leaf). Ghanaian Example: Local tinsmiths take old metal drums and hammer them into thin sheets to make "kɔn-kɔntɛ asanka" (local metal grinding bowls) or coal pots. Aluminum is hammered into roofing sheets. Ductility: The ability of a solid to be drawn into a thin wire. Example: Copper is very ductile, which is why it is perfect for making electrical wires. Ghanaian Example: A goldsmith in the Ashanti region can draw a piece of gold into a very fine thread to be used in making intricate jewelry. Brittleness: The opposite of malleability and ductility. A brittle material breaks or shatters easily when subjected to force, with little to no bending. Example: Glass, chalk, dry clay pot. Ghanaian Example: A clay pot (Adurowa) used for storing water will shatter if it falls. While this seems like a bad property, glass is used for windows because it is also transparent, another important property. Elasticity: The ability of a material to return to its original shape and size after a deforming force is removed. Example: A rubber band or a mattress spring. Ghanaian Example: The rubber used to make "charley wote" (slippers) is elastic, making them flexible and comfortable to walk in. The elastic band in your clothing is another example. B. Thermal Properties (How a material behaves with heat) Thermal Conductivity: This is the measure of how well a material allows heat to pass through it. Good Conductors: Materials that allow heat to pass through them easily (e.g., metals like aluminum, copper, steel). Poor Conductors (Insulators): Materials that do not allow heat to pass through them easily (e.g., wood, plastic, rubber, clay). Ghanaian Example: The body of a cooking pot is made of aluminum (a good conductor) to allow heat from the fire to get to the food quickly. The handles, however, are often made of wood or plastic (insulators) so you can hold the pot without burning your hands. Earthenware pots are poor conductors, so they cook food slowly and keep water cool. C. Electrical Properties (How a material behaves with electricity) Electrical Conductivity: This is the measure of how well a material allows electricity to pass through it. Conductors: Materials that allow electricity to flow through them easily (e.g., metals like copper, silver, aluminum). Insulators: Materials that resist the flow of electricity (e.g., plastic, rubber, wood, glass). Ghanaian Example: The inside of an electrical cable is made of copper (a conductor) to carry the electricity from the powerhouse to our homes. The outside of the cable is coated with plastic (an insulator) to prevent us from getting an electric shock if we touch it.
Summary Table of Properties and Uses
| Property | Meaning | Common Use in Ghana | | ------------------ | ---------------------------------------------- | ------------------------------------------------------ | | Strength | Resists breaking under force | Iron rods and concrete for building construction | | Hardness | Resists scratching and cutting | Steel for cutlass blades; granite for countertops | | Malleability | Can be hammered into thin sheets | Aluminum for roofing sheets; gold for jewelry | | Ductility | Can be drawn into wires | Copper for electrical wiring | | Brittleness | Shatters easily when struck | Glass for windows; chalk for writing | | Elasticity | Returns to original shape after stretching | Rubber for "charley wote" slippers; springs | | Good Conductor | Allows heat/electricity to pass through easily | Aluminum for cooking pots; copper for wires | | Poor Conductor | Blocks the flow of heat/electricity | Plastic/wood for pot handles; plastic for wire coating |