Lesson Notes By Weeks and Term v5 - Grade 9

Lesson Video

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Performance objectives

• Identify and explain principles of structures (frame, shell, solid).
• Describe mechanical systems (levers, gears, pulleys) and calculate MA.
• Identify electronic components and draw a basic circuit diagram.
• Explain open-loop and closed-loop control systems.
• Apply the design process to solve a technological problem.

Lesson summary

This week's focus is dedicated to revising key concepts covered in Technology throughout the term, specifically preparing you for upcoming tests and the final exam. Technology is a crucial subject that helps us understand how things work, design solutions to problems, and improve our world. By mastering these concepts, you'll be better equipped to innovate and contribute to South Africa's future. We'll go through previous topics, practice solving problems, and learn effective study techniques. This includes everything from Structures to Mechanical Systems to Electronics and Control.

Lesson notes

Structures: Structures are anything that holds a load or supports something.

There are three main types: Frame Structures: These are made up of separate parts joined together, like the Eiffel Tower or a bicycle frame. They're strong because the forces are spread throughout the frame. Examples in South Africa include cell phone towers and bridges like the Nelson Mandela Bridge.

Shell Structures: These are hollow and get their strength from their shape, like an eggshell or a dome. Think of the roof of a stadium or a corrugated iron sheet used for roofing in many townships.

Solid Structures: These are made from one solid piece of material, like a brick or a statue. Concrete walls, even if poured, can be considered a solid structure once cured.

Key Considerations for Structures: Strength, Stability, Stiffness (resistance to bending). Consider climate - structures in coastal areas need to resist corrosion from salt air.

Mechanical Systems: Mechanical systems use forces and motion to do work.

The main types we focus on are: Levers: A lever is a rigid bar that pivots around a fixed point called a fulcrum. There are three classes of levers, depending on where the fulcrum, load, and effort are located.

Examples: First Class:* Seesaw (fulcrum in the middle)

Second Class:* Wheelbarrow (load in the middle)

Third Class:* Tweezers (effort in the middle)

Mechanical Advantage (MA): MA = Load / Effort. If MA > 1, the lever makes it easier to lift the load. A crowbar used to lift a rock is a good example.

To calculate MA: MA = Distance from effort to fulcrum / Distance from load to fulcrum Gears: Gears are toothed wheels that transmit rotational motion. When gears mesh together, they change the speed and torque (turning force).

Gear Ratio (GR): GR = Number of teeth on driven gear / Number of teeth on driving gear. If GR > 1, speed decreases but torque increases. Gear systems are used extensively in vehicles, machinery, and even wind turbines, playing a crucial role in various industries across South Africa. If one gear has 20 teeth, and a meshing gear has 40 teeth, the gear ratio is 40/20 =

2. The slower gear is turning with twice the torque.

Pulleys: A pulley is a wheel with a groove around its circumference. A rope or cable runs in the groove. Pulleys can change the direction of a force or provide a mechanical advantage.

Examples: Fixed Pulley:* Changes direction of force (MA = 1) (e.g., a flag pole)

Movable Pulley:* Reduces the amount of force needed to lift a load (MA > 1). A block and tackle system used in construction is an example.

Mechanical Advantage (MA): Number of rope sections supporting the load.

Electronics and Control: Electronics involve the flow of electrons in circuits. Control systems manage how machines and processes operate.

Basic Components: Resistors:* Resist the flow of current (measured in ohms).

LEDs (Light Emitting Diodes):* Emit light when current flows through them. Important for signalling and indicators.

Switches:* Open or close a circuit to control the flow of current.

Batteries:* Provide a source of electrical energy (DC).

Wires:* Conduct electricity.

Circuits: A closed loop that allows electricity to flow.

Series Circuit: Components connected one after the other; current is the same through each component.

Parallel Circuit: Components connected on separate branches; voltage is the same across each component.

Control Systems: Open-Loop System:* No feedback; the output is not measured or used to adjust the input.

Example: A toaster – the heating time is pre-set regardless of how brown the bread is.

Closed-Loop System:* Uses feedback to adjust the input and maintain a desired output.

Example: An air conditioner – it measures the room temperature and adjusts the cooling output to maintain the set temperature. Guided Practice (With Solutions)

Question 1: A crane uses a pulley system to lift a container weighing 5000N. If the pulley system has a mechanical advantage of 5, what effort force is required to lift the container?

Solution: Mechanical Advantage (MA) = Load / Effort.

Therefore, Effort = Load / MA = 5000N / 5 = 1000

N. Commentary: This question directly applies the formula for mechanical advantage. Understanding the relationship between load, effort, and MA is crucial.

Question 2: A gear system has two gears. The driving gear has 25 teeth, and the driven gear has 75 teeth. What is the gear ratio? Is the driven gear turning faster or slower than the driving gear?

Solution: Gear Ratio (GR) = Number of teeth on driven gear / Number of teeth on driving gear = 75 / 25 =

3. Since the gear ratio is greater than 1, the driven gear is turning slower than the driving gear.

Commentary: This question tests your understanding of gear ratios and how they affect speed. Remember that a higher gear ratio means lower speed but higher torque.

Question 3: Draw a simple circuit diagram showing a battery, a switch, a resistor, and an LED connected in series. Label each component.