Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define and identify types of structures and their uses.
• Explain simple mechanisms like levers, pulleys, and gears.
• Describe the components of a simple control system.
• Apply the design process to solve a technological problem.

Lesson summary

This week focuses on revising and consolidating key Technology concepts covered throughout the term. We’ll be revisiting structures, mechanisms, and control systems, emphasizing their practical application in solving everyday problems and innovating solutions within our South African context. Understanding these concepts is vital because technology shapes our world, from the buildings we live in to the tools we use for agriculture and communication. By mastering these fundamental principles, you will develop the problem-solving skills necessary to address challenges and contribute to technological advancements in South Africa.

Lesson notes

2.1 Structures: A structure is something that has a definite size and shape and that can withstand forces.

There are three main types of structures: Mass Structures: These structures rely on their own weight to stay in place. Examples include mountains, dams, and traditional mud houses (rondavels) common in rural South Africa. The thicker the walls of a rondavel, the stronger it is, allowing it to withstand wind and weather.

Frame Structures: These structures consist of a framework of interconnected parts that support a load. Examples include bridges, steel buildings, and even the skeleton of a body. Think of a cellphone tower; it uses a frame to resist wind.

Shell Structures: These structures use a thin, curved outer surface to provide strength and rigidity. Examples include eggs, car bodies, and some roofs. The design of the roof covering the Moses Mabhida Stadium in Durban is a shell structure.

Forces Acting on Structures: Structures must be able to withstand different types of forces, including: Tension: A pulling force.

Compression: A pushing force.

Shear: A force that causes layers to slide past each other.

Torsion: A twisting force.

Bending: A combination of tension and compression.

Example: Consider a simple wooden bench. The legs of the bench are under compression as they support the weight of someone sitting on it. The top of the bench experiences bending. The screws holding the bench together need to resist shear. 2.2 Mechanisms: A mechanism is a device that changes motion or force.

Simple mechanisms include: Levers: A rigid bar that pivots around a fixed point (fulcrum). Levers are used to multiply force.

Mechanical Advantage (MA) of a Lever: MA = Load / Effort = Distance from Effort to Fulcrum / Distance from Load to Fulcrum

Example: Using a crowbar (lever) to lift a heavy rock. If the distance from the fulcrum to where you apply force (effort) is 1 meter, and the distance from the fulcrum to the rock (load) is 0.2 meters, then the MA = 1/0.2 =

5. This means you can lift a rock that weighs 5 times the force you apply.

Pulleys: A wheel with a grooved rim around which a rope passes. Pulleys can be used to change the direction of a force or to multiply force.

Mechanical Advantage (MA) of a Pulley: For a single fixed pulley, MA = 1 (changes direction only). For a movable pulley or a block and tackle system, MA = Number of rope segments supporting the load.

Example: Construction workers using a pulley system to lift building materials.

Gears: Toothed wheels that mesh together to transmit rotary motion and force. Gears can change the speed and torque of a rotating object.

Gear Ratio: Number of teeth on the driven gear / Number of teeth on the driving gear.

Example: In a bicycle, the gears allow you to pedal at a comfortable rate while travelling at different speeds. 2.3 Control Systems: A control system is a system that regulates or controls another system. Control systems have three basic components: Input: Something that tells the system what to do.

Process: What the system does with the input.

Output: The result of the process.

Example: A simple thermostat controls the temperature in a room.

Input: The desired temperature set on the thermostat.

Process: The thermostat compares the actual temperature to the desired temperature and switches the heater on or off.

Output: The heater turns on or off, changing the room temperature.

Another example is a traffic light system: Input: Sensors detecting the presence of cars.

Process: The traffic light controller uses pre-programmed timing or sensor data to determine which lights should be green, yellow, or red.

Output: The traffic lights changing color. 2.4 The Design Process: The design process is a systematic approach to solving technological problems.

It typically involves the following steps: Investigation: Identify and define the problem. Research existing solutions.

Design: Brainstorm possible solutions. Develop a detailed design, including sketches and specifications.

Making: Build a prototype of the design.

Evaluation: Test the prototype and identify areas for improvement.

Communication: Share the design and results with others. Guided Practice (With Solutions)

Question 1: Identify the type of structure used in a traditional Zulu hut (rondavel) and explain why this type of structure is well-suited for the South African climate.

Solution: The traditional Zulu hut (rondavel) is primarily a mass structure. The thick walls are made of earth or clay, relying on their weight to provide stability and insulation. This type of structure is well-suited for the South African climate because the thick walls provide excellent insulation, keeping the hut cool during hot summer days and warm during cold winter nights. The circular shape also helps to distribute wind forces evenly, making it more resistant to strong winds common in some parts of the country.

Question 2: A lever is used to lift a heavy box.