Lesson Notes By Weeks and Term v4 - JHS 2

Lesson Video

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Performance objectives

• Identify at least three examples of complex machines.
• Describe the function of each identified complex machine.
• Explain how forces act on these machines to make them work.
• Analyze the advantages of using complex machines.

Lesson summary

In everyday life in Ghana, people use machines to make work easier—pounding fufu with a mortar and pestle, drawing water from a well, using a wheelbarrow at a building site, using a bicycle, a sewing machine, a can opener, or a cassava grater. Many of these are complex machines (also called compound machines) made by combining two or more simple machines. Understanding complex machines helps learners to: work safely and efficiently, choose the right tool for a job, appreciate local technologies (e.g., gari processing, carpentry, construction), understand how force and motion are controlled in machines.

Lesson notes

A. Force and Motion (Quick Reminder) Force is a push or pull that can start motion, stop motion, change speed, or change direction. Motion is the movement of an object from one place to another. Machines help us manage force to produce desired motion more easily. B. Simple Machines (Building Blocks) A simple machine is a device that makes work easier by changing: the size of the force (making a small effort lift a big load), or the direction of the force, or the distance/speed over which the force acts.

Common simple machines (JHS level): Lever (e.g., crowbar, seesaw) Pulley (e.g., rope and wheel at a well) Wheel and axle (e.g., bicycle wheel, doorknob) Inclined plane (e.g., ramp) Wedge (e.g., cutlass blade, axe) Screw (e.g., bolt, jar lid, wood screw) C. Meaning of Complex (Compound) Machines A complex machine is a machine made by combining two or more simple machines working together to perform a task.

Key idea: Complex machines make work easier because each simple machine part contributes to: multiplying force (reducing effort), changing direction of force, increasing speed or distance, improving control and safety. D. How to Identify a Complex Machine (Step-by-step) When you see a tool/device, ask: What is the job? (lifting, cutting, moving, fastening, grinding) Which simple machine parts can I see? Is there a wheel and axle? Is there a lever arm? Is there a screw thread? Is there a wedge blade? Is there a pulley wheel? Are there at least two simple machines? If yes, it is a complex machine. E. Examples of Complex Machines in Ghana (with parts and explanations) 1) Wheelbarrow (common at building sites and farms) Simple machines inside: Lever: the handles act as a lever to lift the load. Wheel and axle: the front wheel reduces friction and makes movement easier.

How it helps (force and motion): The lever reduces the effort needed to lift the load. The wheel reduces friction, allowing smooth motion over the ground. 2) Bicycle Simple machines inside: Wheel and axle: wheels rotate around axles. Levers: brake levers and pedal cranks act like levers. Gears (wheel and axle concept): help change speed and force. Screws/bolts: hold parts firmly.