Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Apply principles of levers, pulleys, and gears.
• Explain properties and uses of engineering materials.
• Demonstrate understanding of basic electricity principles.
• Calculate mechanical advantage, velocity ratio, and efficiency.
• Identify and apply workshop safety procedures.

Lesson summary

This week focuses on consolidating our understanding of key concepts covered throughout the term in Mechanical Technology. Solid examination preparation involves more than just memorization; it requires a deep understanding of the principles, the ability to apply them to solve problems, and the confidence to articulate your knowledge clearly. In the South African context, a strong foundation in Mechanical Technology opens doors to diverse career paths in manufacturing, engineering, and infrastructure development – all crucial for our nation's economic growth. Mastering these concepts now sets the stage for more advanced studies and future success.

Lesson notes

This section covers the key concepts for examination preparation.

A. Mechanical Systems (Levers, Pulleys, Gears): Levers: A lever is a rigid bar that pivots about a fixed point called a fulcrum. Levers amplify force.

Classes of Levers: Class 1: Fulcrum is between the effort and the load (e.g., see-saw, crowbar). Mechanical Advantage (MA) can be >1,

1. Class 3: Effort is between the fulcrum and the load (e.g., tweezers, fishing rod). MA is always <

1. Mechanical Advantage (MA): The ratio of load (L) to effort (E): MA = L/E Velocity Ratio (VR): The ratio of the distance moved by the effort (DE) to the distance moved by the load (DL): VR = DE/DL Efficiency (η): The ratio of mechanical advantage to velocity ratio, expressed as a percentage: η = (MA/VR) 100% Example 1 (Lever): A builder uses a 2m crowbar to lift a concrete slab weighing 500

N. The fulcrum is placed 0.5m from the slab. Calculate the effort required.

Solution: This is a Class 1 lever. Load (L) = 500N Load distance (DL) = 0.5m Effort distance (DE) = 2m - 0.5m = 1.5m Using the principle of moments: Effort x Effort distance = Load x Load distance Effort x 1.5m = 500N x 0.5m Effort = (500N x 0.5m) / 1.5m = 166.67N Pulleys: Pulleys use grooved wheels and ropes to change the direction of a force and, in some cases, multiply the force.

Types of Pulleys: Fixed pulleys (change direction only), Movable pulleys (multiply force).

Velocity Ratio (VR): For a pulley system, the VR is equal to the number of rope segments supporting the load.

Example 2 (Pulleys): A hoisting system uses 4 rope segments to support a load of 800

N. If the effort required is 250N, calculate the mechanical advantage and efficiency.

Solution: Mechanical Advantage (MA) = Load / Effort = 800N / 250N = 3.2 Velocity Ratio (VR) = 4 (number of rope segments) Efficiency (η) = (MA / VR) 100% = (3.2 / 4) 100% = 80% Gears: Gears are toothed wheels that transmit rotational motion and force.

Velocity Ratio (VR): For two meshing gears, VR = Number of teeth on the driven gear / Number of teeth on the driving gear. If VR is greater than 1, the output speed is lower than the input speed, but the output torque (turning force) is higher. If VR is less than 1, the output speed is higher, and the output torque is lower.

Example 3 (Gears): A driving gear with 20 teeth meshes with a driven gear with 60 teeth. If the driving gear rotates at 120 rpm, what is the rotational speed of the driven gear?

Solution: Velocity Ratio (VR) = Number of teeth on driven gear / Number of teeth on driving gear = 60 / 20 = 3 VR = Speed of driving gear / Speed of driven gear 3 = 120 rpm / Speed of driven gear Speed of driven gear = 120 rpm / 3 = 40 rpm

B. Engineering Materials: Ferrous Metals: Metals containing iron (e.g., steel, cast iron). Prone to rust.

Non-Ferrous Metals: Metals that do not contain iron (e.g., aluminum, copper, brass). Generally more resistant to corrosion.

Polymers (Plastics): Long-chain molecules, often derived from petroleum. Can be thermoplastic (soften with heat) or thermosetting (set permanently with heat).

Examples: PVC pipes (used widely in South Africa for plumbing), polyethylene bags.

Composites: Materials made by combining two or more different materials to achieve desired properties (e.g., fiberglass - glass fibers in a polymer matrix). Strong and lightweight.

Example: Selection of materials for a water pipe. Consider factors such as cost, availability (locally sourced is preferable in South Africa), corrosion resistance, pressure rating, and ease of installation. PVC is often used due to its affordability and ease of installation, while copper might be used in situations requiring higher pressure resistance.

C. Basic Electricity: Ohm's Law: V = IR (Voltage = Current x Resistance)

Series Circuits: Components are connected one after the other, so the current is the same throughout. The total resistance is the sum of the individual resistances (RT = R1 + R2 + ...). The voltage is divided across the components.

Parallel Circuits: Components are connected side-by-side, so the voltage is the same across each component. The current divides between the branches. The reciprocal of the total resistance is the sum of the reciprocals of the individual resistances (1/RT = 1/R1 + 1/R2 + ...).

Example 4 (Ohm's Law): A light bulb has a resistance of 240 ohms and is connected to a 240V power supply. What is the current flowing through the bulb?

Solution: V = IR 240V = I x 240 ohms I = 240V / 240 ohms = 1 Ampere

D. Workshop Safety: Always wear appropriate personal protective equipment (PPE) such as safety glasses, overalls, and closed shoes. Keep the workspace clean and tidy to prevent slips and falls. Use tools correctly and for their intended purpose. Report any damaged tools or equipment immediately. Know the location of fire extinguishers and first aid kits. Never operate machinery without proper training and authorization. Guided Practice (With Solutions)

Question 1: A mechanic uses a lever to lift an engine.