Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• This week, we're consolidating our understanding of key Technology concepts we've covered this year. Technology is all around us, from the phones we use to communicate to the complex systems that bring electricity to our homes and clean water to our taps. This isn't just about gadgets; it's about using knowledge and skills to solve problems and improve our lives and the lives of our communities in South Africa. We’ll specifically focus on structures (frames and shells), systems and control, and mechanical systems. Understanding these topics allows you to design better solutions to local challenges, perhaps inventing a more efficient water filter or designing stronger, more affordable housing.
• By the end of this week, you should be able to:
• LO1: Identify and classify different types of structures (frames and shells) based on their shapes, materials, and intended functions. (CAPS: Design Skills, Technological Knowledge and Understanding)
• LO2: Explain the principles of systems and control, including input, process, and output, using practical South African examples. (CAPS: Technological Knowledge and Understanding)
• LO3: Describe the function of basic mechanical systems (levers, gears, pulleys) and explain how they transfer force and motion. (CAPS: Technological Knowledge and Understanding)

Lesson summary

This week, we're consolidating our understanding of key Technology concepts we've covered this year. Technology is all around us, from the phones we use to communicate to the complex systems that bring electricity to our homes and clean water to our taps. This isn't just about gadgets; it's about using knowledge and skills to solve problems and improve our lives and the lives of our communities in South Africa. We’ll specifically focus on structures (frames and shells), systems and control, and mechanical systems.

Lesson notes

2.1 Structures: Frames and Shells Structures are things that support loads and resist forces.

We'll focus on two main types: frames and shells.

Frames: Frames are structures made up of individual members (like beams and columns) connected together to form a network. Think of a bicycle frame, a bridge, or the steel skeleton of a building. The strength of a frame comes from the arrangement of its members and the materials used. Triangles are very important in frames because they are a rigid shape that doesn't easily deform.

Examples: The Nelson Mandela Bridge in Johannesburg is a frame structure. So is the framework of a soccer stadium. In our homes, a Wendy house's wooden frame is another example.

Materials: Common materials include steel, wood, and reinforced concrete. The choice depends on the load, the environment (e.g., coastal areas need corrosion-resistant materials), and the budget.

Shells: Shells are structures that rely on their shape to distribute loads. Think of an eggshell, a dome, or even a corrugated iron roof. Shells are strong because the stresses are spread evenly throughout the material.

Examples: The roof of a soccer stadium is often a shell structure. A corrugated iron shack is a shell, albeit a less efficient one. Plastic bottles can be surprisingly strong because of their shell-like shape. The rondavel (traditional African hut) is a shell structure.

Materials: Shells can be made from concrete, metal, plastic, or even natural materials like mud bricks. The material needs to be strong enough to withstand the stresses, but also flexible enough to be formed into the desired shape. Worked

Example: Consider a corrugated iron sheet used for a shack roof. Why is it corrugated (wavy)? The corrugations increase the sheet's stiffness and resistance to bending. This makes it a stronger shell structure than a flat sheet of iron, which would easily buckle under load. What forces act on it? Wind pressure, the weight of rainwater, and potentially even people walking on it. How could we make it stronger? By using thicker iron, adding more corrugations, or supporting it with a frame underneath. 2.2 Systems and Control A system is a set of interacting components that work together to achieve a specific goal. A control system is a system that regulates itself to maintain a desired output.

The basic parts of a system are: Input: Something that is put into the system (e.g., pressing a button, turning a tap).

Process: What happens inside the system (e.g., a motor turning, water flowing through pipes).

Output: What comes out of the system (e.g., a light turning on, water coming out of the tap).

Example: A simple water tap is a system.

Input: Turning the tap handle.

Process: The valve inside the tap opens, allowing water to flow through the pipes.

Output: Water flows out of the tap.

Example: A security gate with remote control.

Input: Pressing the button on the remote control.

Process: A signal is sent to the gate motor, which activates and opens or closes the gate.

Output: The gate opens or closes.

Control Systems: These systems have feedback loops to adjust the process based on the output. Think of a geyser thermostat that turns the heating element on and off to maintain a constant water temperature. Worked

Example: Consider a simple burglar alarm system in a house.

Input: A sensor detects movement or a door opening.

Process: The sensor sends a signal to the alarm control panel, which triggers the siren.

Output: A loud siren sounds, alerting occupants and neighbors.

Control (Feedback): More sophisticated alarm systems might have feedback. For example, if the siren is silenced by entering a code, the system may log the event or send a notification to a security company. 2.3 Mechanical Systems: Levers, Gears, and Pulleys Mechanical systems use simple machines to transfer and modify force and motion.

Levers: A lever is a rigid object that pivots around a fixed point called a fulcrum. Levers are used to multiply force. There are three classes of levers, defined by the relative positions of the fulcrum, the load (the thing being moved), and the effort (the force applied).

Example: A see-saw (class 1 lever), a wheelbarrow (class 2 lever), a pair of tongs (class 3 lever).

Gears: Gears are toothed wheels that mesh together to transmit rotational motion and torque (turning force). Gears can change the speed, direction, and force of rotation.

Example: A bicycle's gears allow you to pedal at a comfortable rate even when going uphill or downhill.

Pulleys: A pulley is a wheel with a grooved rim around which a rope or cable passes. Pulleys are used to change the direction of force and can also be used to multiply force (depending on the pulley arrangement).

Example: A flagpole uses a pulley to make it easier to raise and lower the flag. Construction workers use pulleys to lift heavy materials. Worked

Example: Bicycle Gears How do gears work? The gear connected to the pedals is called the chainring.