Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Identify and describe different types of structures.
• Explain the function of different mechanisms like levers, gears, and pulleys.
• Differentiate between open-loop and closed-loop systems.
• Understand and construct simple electrical circuits.
• Apply safe working practices with tools and electricity.

Lesson summary

This week is dedicated to revising and consolidating key concepts covered throughout Grade 7 Technology. Technology is not just about computers; it's about using knowledge and resources to solve problems and create things that improve our lives. In South Africa, understanding technology is vital for developing innovative solutions to challenges like water scarcity, electricity access, and efficient transportation. This revision week ensures a solid foundation for future learning and empowers you to become problem-solvers in your communities.

Lesson notes

Structures: Structures are things that support a load and maintain their shape.

There are three main types: Frame Structures: These structures are made of interconnected parts that support a load. They are strong and lightweight because the load is distributed across the frame. Examples include bridges, cellphone towers, and the skeleton of a building. Think of the Nelson Mandela Bridge in Johannesburg; it's a massive frame structure designed to withstand immense weight and wind forces. In a smaller, more familiar context, the frame of a bicycle is also a frame structure.

Shell Structures: These structures are hollow and rely on their shape to provide strength and stability. Examples include eggs, domes, and cans. The Union Buildings in Pretoria, with their distinctive dome, is a shell structure on a grand scale. Even a plastic water bottle relies on its shell shape for strength.

Solid Structures: These are made from a single, solid piece of material. They are strong but can be heavy. Examples include walls, dams, and statues. The Great Zimbabwe ruins are examples of solid structures made from stacked stones. A brick used in a building is a smaller example.

Mechanisms: Mechanisms are devices that change the direction or magnitude of a force. Understanding mechanisms helps us design machines that make work easier.

Levers: A lever is a rigid bar that pivots around a fixed point (fulcrum) to multiply force. There are three classes of levers, depending on the placement of the load, effort, and fulcrum. Think of a see-saw (a Class 1 lever), a wheelbarrow (a Class 2 lever), and a pair of tongs (a Class 3 lever). A crowbar used to lift a heavy object is a common example of a lever in South Africa. Mechanical Advantage (MA) = Load / Effort. A higher MA means less effort is needed to move the same load.

Gears: Gears are toothed wheels that mesh together to transmit rotational motion and force. Gears can change the speed, torque, or direction of rotation. A bicycle uses gears to make it easier to pedal uphill or to go faster on flat ground. Gear ratios determine the speed and torque relationship between gears. Gear Ratio = Number of teeth on driven gear / Number of teeth on driving gear. A gear ratio greater than 1 means the driven gear rotates slower but with more torque. A gear ratio less than 1 means the driven gear rotates faster but with less torque. Speed Ratio = Number of rotations of driver gear / Number of rotations of driven gear.

Pulleys: A pulley is a wheel with a grooved rim that a rope, cable, or belt runs along. Pulleys are used to lift heavy objects or transmit force. A simple pulley system can change the direction of the force, making it easier to lift objects. Complex pulley systems can provide mechanical advantage. Imagine construction workers using a pulley system to lift building materials onto a construction site.

Systems and Control: Systems: A system is a group of interacting components that work together to achieve a specific purpose. In technology, we often design systems to automate tasks or control processes.

Open-loop Systems: These systems operate without feedback. The output is not measured or used to adjust the input. A simple toaster is an example of an open-loop system. You set the timer, and the toaster toasts the bread for that amount of time, regardless of how brown the bread actually gets.

Closed-loop Systems: These systems use feedback to control the output. A sensor measures the output, and this information is used to adjust the input to maintain the desired output. A thermostat in a house is a closed-loop system. It measures the temperature and turns the heater on or off to maintain the set temperature. An irrigation system in a farm uses a soil moisture sensor to automatically water the plants when the soil is dry.

Electrical Systems: Circuits: An electrical circuit is a closed path through which electric current flows. A simple circuit consists of a power source (battery), a conductor (wire), and a load (light bulb).

Components: Battery: Provides the voltage (electrical potential difference) that drives the current.

Switch: Opens and closes the circuit, allowing or preventing current flow.

Resistor: Limits the current flow.

LED (Light Emitting Diode): Emits light when current flows through it in the correct direction.

Series Circuits: Components are connected one after another, so the same current flows through each component.

Parallel Circuits: Components are connected in separate branches, so the current divides between the branches.

Worked example

Gear Ratio Calculation: A gear system has a driving gear with 20 teeth and a driven gear with 40 teeth. What is the gear ratio?

Solution: Gear Ratio = Number of teeth on driven gear / Number of teeth on driving gear = 40 / 20 =

2. This means the driven gear rotates slower than the driving gear but with more torque.

Lever Calculation: A person uses a crowbar (Class 1 lever) to lift a rock. The distance from the fulcrum to the rock (load) is 0.5 meters, and the distance from the fulcrum to the point where the person applies force (effort) is 1.5 meters. If the rock weighs 300 N, what force (effort) is needed to lift the rock, assuming ideal conditions (no friction)?

Solution: We can use the principle of moments (Torque). Effort x Effort arm = Load x Load Arm.

Therefore, Effort x 1.5m = 300N x 0.5m. Effort = (300N x 0.5m) / 1.5m = 100N. The person needs to apply a force of 100N. Mechanical Advantage is 300N/100N =

3. Simple Electrical Circuit: Design a circuit using a 9V battery, a switch, a 100 Ohm resistor, and an LE

D. Solution: Connect the positive terminal of the battery to one side of the switch. Connect the other side of the switch to one end of the resistor. Connect the other end of the resistor to the positive (longer) leg of the LED. Connect the negative (shorter) leg of the LED to the negative terminal of the battery. The resistor limits the current to prevent the LED from burning out. Closing the switch will complete the circuit and light up the LED.

Guided Practice (With Solutions)

Question: Identify the type of structure used to build a typical South African RDP house (Reconstruction and Development Programme). Explain your choice.

Solution: RDP houses typically utilize a frame structure and solid structure combination. The walls are built from bricks or blocks (solid structure), providing the primary support. The roof often has a frame structure, with wooden or metal beams supporting the roofing material. The walls act as the foundation for the frame structure.

Question: A gear system has a driving gear with 15 teeth rotating at 60 RPM (revolutions per minute). The driven gear has 30 teeth. What is the speed (RPM) of the driven gear?

Solution: Speed Ratio = Number of rotations of driver gear / Number of rotations of driven gear. Gear Ratio = Number of teeth on driven gear / Number of teeth on driving gear = 30/15 =

2. Speed ratio = 1/Gear ratio. Speed ratio = 1/2 = 0.

5. Therefore, Number of rotations of driven gear = Number of rotations of driver gear/ Speed ratio = 60 RPM/2 = 30RP

M. Question: Explain how a solar geyser uses both system and control concepts (open-loop and closed-loop).

Solution: A basic solar geyser can be considered an open-loop system. Sunlight heats the water in the collector, and the hot water rises to the tank.

However, the water temperature might get too high or stay cold on cloudy days. A more sophisticated solar geyser incorporates a closed-loop system. A temperature sensor in the tank provides feedback to a controller. If the water is too cold, the controller might activate an auxiliary electric heater until the desired temperature is reached.

Question: Draw a circuit diagram showing a battery connected to two LEDs in parallel, each with its own resistor. Explain why resistors are needed.

Solution: The circuit diagram should show a battery. From the positive terminal, the circuit splits into two branches. Each branch contains a resistor and an LED connected in series. The negative legs of the LEDs are then connected back to the negative terminal of the battery. Resistors are crucial to limit the current flowing through each LED. LEDs are sensitive to overcurrent and will burn out quickly without a suitable resistor to protect them.

Independent Practice (Questions Only)

Describe three examples of frame structures found in your local community.

A lever is used to lift a heavy box. The load is 400 N and is placed 0.4 meters from the fulcrum. If the effort is applied 2 meters from the fulcrum, what is the effort required to lift the box?

A gear system has a driving gear with 48 teeth and a driven gear with 12 teeth. If the driving gear rotates at 20 RPM, what is the speed of the driven gear? Is this a speed increasing or speed decreasing configuration?

Explain the difference between an open-loop and closed-loop control system using the example of a security gate at a shopping mall.

Draw a circuit diagram showing a battery, a switch, and three light bulbs connected in series. What happens if one of the light bulbs burns out?

Design a system for alerting people about a water leak in their house. Describe the sensors, actuators, and control system involved.

Explain why shell structures are so commonly used for roofing in South Africa.

A crane uses a pulley system to lift shipping containers at a port. Explain how the pulley system makes the job easier and safer. What class of lever system would the controls likely use for operation by the crane operator?

Consider a solar water heating system. What are the energy inputs and outputs of the system? What are the potential benefits and drawbacks of using this technology in a South African context?