Lesson Notes By Weeks and Term v5 - Grade 9

Lesson Video

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Performance objectives

• Explain key concepts: structures, mechanisms, and control systems.
• Apply the design process to solve problems.
• Analyze the impact of technology.
• Create accurate technical drawings.
• Critically evaluate existing technologies.

Lesson summary

This week is dedicated to revising and preparing for the upcoming Technology exams. Technology is a crucial subject that equips you with the knowledge and skills to solve problems, design innovative solutions, and understand the world around you. From designing a more efficient water collection system in your community to understanding the mechanics of the taxi you take to school, Technology is everywhere! This revision week allows us to consolidate our understanding of the concepts covered throughout the term and practice applying them to various scenarios.

Lesson notes

This week's revision will focus on the following key areas: Structures: Understanding different types of structures (e.g., frame, shell, solid), their properties (strength, stability, rigidity), and how different materials affect these properties.

Mechanisms: Exploring different types of mechanisms (e.g., levers, linkages, gears, pulleys), their mechanical advantage, and how they transfer and transform motion.

Control Systems: Investigating different types of control systems (e.g., manual, automatic, open-loop, closed-loop), their components (e.g., sensors, actuators, controllers), and how they regulate processes.

Materials and Manufacturing: Understanding the properties of different materials (e.g., metals, plastics, wood, composites), common manufacturing processes (e.g., cutting, joining, shaping), and sustainable material choices.

Design Process: Revisiting the stages of the design process (Investigating, Designing, Making, Evaluating, Communicating) and understanding how to apply them effectively to solve technological problems.

Technical Drawings: Mastering the principles of orthographic projection and isometric drawing to accurately represent designs.

Detailed Explanations: Structures: A structure is anything that supports a load.

There are three main types: Solid Structures: These are made from a single, solid piece of material (e.g., a brick wall, a solid wooden table). Their strength depends on the material and its shape.

Frame Structures: These are made from individual members joined together to form a framework (e.g., a bridge, a steel building). Frame structures are strong because the load is distributed among the members. Triangles are commonly used because they are very rigid shapes.

Shell Structures: These are made from a thin, curved shell of material (e.g., an eggshell, a plastic bottle). Shell structures are strong because the curved shape distributes the load evenly.

Example: Think about a rondavel (traditional African hut). The walls are typically solid structures made of mud bricks, providing stability. The roof is often a conical frame structure, with poles supporting a covering of thatch or corrugated iron.

Mechanisms: A mechanism is a device that transmits and transforms motion.

Levers: A lever is a rigid bar that pivots around a fixed point called a fulcrum. Levers are used to amplify force (mechanical advantage). There are three classes of levers, depending on the relative positions of the load, fulcrum, and effort.

Example: A see-saw is a class 1 lever. Effort (pushing down), Fulcrum (the pivot point), and Load (the person being lifted).

Linkages: A linkage is a series of rigid links connected by joints. Linkages are used to transmit motion over a distance or to change the direction of motion.

Example: The linkages in a bicycle's brakes convert the linear motion of your hand into the rotational motion that stops the wheels.

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

Example: Gears in a bicycle allow you to pedal at a comfortable speed while the wheels turn faster, allowing you to move faster.

Pulleys: A pulley is a wheel with a grooved rim around which a rope, cable, or belt passes. Pulleys are used to lift heavy objects or to transmit power.

Example: Using a pulley system to lift buckets of water from a well reduces the effort needed.

Control Systems: A control system is a system that regulates a process or device.

Manual Control: The operator directly controls the system (e.g., turning on a tap).

Automatic Control: The system automatically regulates itself without human intervention (e.g., a thermostat controlling the temperature of a room).

Open-Loop Control: The system does not receive feedback about the output (e.g., a toaster – it runs for a set time regardless of whether the bread is toasted).

Closed-Loop Control: The system receives feedback about the output and adjusts the input accordingly (e.g., a geyser – it heats the water to a set temperature and then switches off).

Example: Consider a traffic light system. Early systems were manual, controlled by a police officer. Modern systems are automatic, with timers and sensors adjusting the lights based on traffic flow (closed-loop).

Mathematics/Science example: Calculating Mechanical Advantage (MA) of a Lever: MA = Load / Effort

Example: A person uses a lever to lift a rock. The rock (load) weighs 500N. The person applies a force (effort) of 100N. MA = 500N / 100N = 5 The mechanical advantage is

5. This means the lever multiplies the person's force by

5. Technical Drawings: Orthographic Projection: Shows multiple 2D views of an object (front, top, side) to fully define its shape and dimensions.

Isometric Drawing: A 3D representation of an object where all three axes are equally foreshortened. Angles are drawn at 30 degrees to the horizontal.

Worked example

Imagine you need to design a simple wooden stool.

Design Process: You would first Investigate the need for a stool (e.g., for sitting comfortably while working). You would then Design the stool, considering its size, shape, and materials. You would then Make the stool, using appropriate tools and techniques. You would then Evaluate the stool, checking its stability, comfort, and appearance. Finally, you would Communicate your design through technical drawings and a written report.

Structures: The stool would be a frame structure, with legs supporting a seat.

Materials: You could use wood for the legs and seat. Consider the properties of different types of wood (e.g., pine is lightweight but less strong than oak).

Technical Drawing: You would create an orthographic projection showing the front, top, and side views of the stool, including dimensions. You would also create an isometric drawing to visualize the stool in 3D.

Guided Practice (With Solutions)

Question 1:

A builder needs to lift a heavy concrete block (400N) using a lever. They can apply a force of 100N. What is the mechanical advantage of the lever they need to use?

Solution: