Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Identify and explain different types of mechanical systems.
• Apply the concepts of input, process, and output.
• Describe the properties and applications of different materials.
• Understand basic principles of electrical circuits.
• Draw and interpret basic technical drawings.

Lesson summary

This lesson focuses on revising and consolidating key concepts covered in Grade 7 Technology thus far, with a particular emphasis on topics typically addressed in the first 4 weeks of the term (adjust as per your actual curriculum pacing). This is crucial because it helps you solidify your understanding of the foundational principles upon which more advanced concepts will be built later in the year. A strong grasp of these concepts will not only improve your performance in assessments but also enable you to apply your knowledge to solve real-world problems, design innovative solutions, and contribute meaningfully to South Africa's technological advancement.

Lesson notes

2.1 Mechanical Systems: Mechanical systems are combinations of parts that work together to perform a specific task. They convert energy from one form to another or transfer forces. Understanding how these systems function is vital for designing and improving various tools and machines we use daily.

Lever Systems: A lever is a rigid bar that pivots around a fixed point called a fulcrum. Levers help us multiply force, making it easier to lift heavy objects or perform tasks. There are three classes of levers, defined by the relative positions of the fulcrum, load (resistance), and effort (force).

First-class lever:* Fulcrum between the load and the effort (e.g., seesaw, crowbar).

Second-class lever:* Load between the fulcrum and the effort (e.g., wheelbarrow, bottle opener).

Third-class lever:* Effort between the fulcrum and the load (e.g., tweezers, fishing rod).

Example: Using a crowbar (first-class lever) to lift a heavy rock. The fulcrum is a small stone placed near the rock. The effort is the force you apply to the other end of the crowbar. The load is the weight of the rock. Because the fulcrum is closer to the rock, a relatively small effort can move a large rock.

Pulley Systems: A pulley is a wheel with a grooved rim around which a rope or cable runs. Pulleys can change the direction of a force or multiply force, making it easier to lift or move heavy objects.

Fixed pulley:* Changes the direction of the force but does not multiply it. (e.g., a flagpole pulley)

Movable pulley:* Multiplies the force but does not change the direction.

Block and tackle:* A combination of fixed and movable pulleys, providing significant mechanical advantage (force multiplication).

Example: Using a block and tackle system (combination of fixed and movable pulleys) to lift a bucket of water from a well. The more pulleys in the system, the less effort is required, but the distance the rope needs to be pulled increases. This is particularly relevant in rural South Africa, where wells are still a common source of water.

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

Driving gear:* The gear that provides the input force.

Driven gear:* The gear that receives the output force.

Gear ratio:* The ratio of the number of teeth on the driven gear to the number of teeth on the driving gear. A gear ratio greater than 1 increases torque but decreases speed, and a gear ratio less than 1 increases speed but decreases torque.

Example: A bicycle uses gear systems. When you pedal, the driving gear (connected to the pedals) turns a smaller driven gear (connected to the rear wheel). This increases the speed of the bicycle, allowing you to travel faster. Shifting gears changes the gear ratio, allowing you to climb hills more easily (higher torque, lower speed) or travel even faster on flat ground (lower torque, higher speed). 2.2 Input, Process, and Output: Every technological system can be broken down into three basic components: Input: The resources (materials, energy, information) that enter the system.

Process: The actions or operations that transform the input into the desired output.

Output: The result of the process; the desired product or service.

Example: A simple bread-making system.

Input:* Flour, water, yeast, salt, oven, electricity, baker's effort.

Process:* Mixing ingredients, kneading dough, allowing dough to rise, baking in the oven.

Output:* Baked bread. 2.3 Material Properties: Understanding the properties of materials is essential for choosing the right material for a specific application.

Key properties include: Strength: Ability to withstand force without breaking (tensile, compressive, shear strength).

Hardness: Resistance to scratching or indentation.

Durability: Ability to withstand wear and tear over time.

Flexibility: Ability to bend without breaking.

Conductivity: Ability to conduct heat or electricity.

Density: Mass per unit volume.

Example: Choosing a material for building a school desk. You would need a material with high strength and durability (e.g., hardwood or steel) to withstand the weight and wear and tear from students. 2.4 Electrical Circuits: An electrical circuit is a closed loop that allows electricity to flow.

Key components include: Power Source: Provides the electrical energy (e.g., battery, generator).

Conductor: Allows electricity to flow easily (e.g., copper wire).

Load: Uses the electrical energy to perform a task (e.g., light bulb, motor).

Switch: Opens or closes the circuit to control the flow of electricity.

Series Circuit: Components are connected in a single loop. If one component fails, the entire circuit breaks.

Parallel Circuit: Components are connected in multiple loops. If one component fails, the other components continue to function.

Example: A string of Christmas lights. If they are wired in series, if one bulb blows, the entire string goes out.