Lesson Notes By Weeks and Term v3 - Primary 6
(ii) Pulleys
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(ii) Pulleys
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Subject: Basic Technology
Class: Primary 6
Term: 3rd Term
Week: 2
Theme: You And Energy
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recognize and identify simple pulley machines identify and describe the different uses of pulley machines in everyday life distinguish between fixed and movable pulleys make and use pulley machines to do work
A. What is a Pulley? A pulley is a simple machine consisting of a wheel with a grooved rim (called a sheave) over which a rope, chain, or cable passes. Pulleys are used to lift heavy objects, change the direction of a force, or transmit power. They are designed to make work easier by reducing the effort required to move a load.
B. Parts of a Simple Pulley A simple pulley typically comprises three main parts:
1. Wheel (Sheave): The circular part that rotates. It usually has a groove around its edge to guide the rope.
2. Axle: The rod or shaft around which the wheel rotates. It is fixed to the frame.
3. Rope/Cable: The flexible material (e.g., nylon rope, wire cable) that runs over the wheel, connecting the effort (force applied) to the load (object being lifted). C. How Pulleys Work Pulleys work by distributing the weight of a load over a longer distance, thereby reducing the amount of force (effort) needed to lift it. This principle is known as mechanical advantage.
Effort: The force applied to the rope to move the load.
Load: The weight of the object being lifted.
Mechanical Advantage (MA): The ratio of the load lifted to the effort applied. A pulley system with a mechanical advantage greater than 1 means less effort is needed to lift the same load.
D. Types of Pulleys
1. Fixed Pulley: Description: A pulley that is attached to a support structure and remains stationary (does not move up or down) when the load is lifted. The axle is fixed in position.
Function: Its primary function is to change the direction of the force applied. For example, pulling down on a rope to lift a load upwards is often more convenient than pulling upwards.
Mechanical Advantage: A single fixed pulley provides a mechanical advantage of approximately 1 (MA ≈ 1). This means the effort required is roughly equal to the weight of the load. It does not reduce the effort needed, only changes the direction of the force. Nigerian
Examples: Raising a flag on a flagpole during a school assembly or national events. Lifting a bucket of water from a well, where one pulls downwards to bring the bucket up. Window blinds or curtains that use a cord to pull them up or across.
2. Movable Pulley: Description: A pulley that is attached directly to the load and moves along with it when the load is lifted or lowered. The rope is attached to a fixed support at one end, passes around the pulley, and the effort is applied to the other end of the rope.
Function: Its primary function is to reduce the effort required to lift a load. It effectively doubles the force, meaning you need only half the effort to lift the same weight (ideally). It also changes the direction of the force.
Mechanical Advantage: A single movable pulley provides a mechanical advantage of approximately 2 (MA ≈ 2). This means the effort needed is roughly half the weight of the load. Nigerian
Examples: Construction workers using a rope and a pulley attached to the load (e.g., cement bag) to lift materials to higher floors. Mechanics lifting heavy car engines or components in a workshop. Part of a more complex block and tackle system used in loading/unloading cargo from trucks or boats.
3. Block and Tackle System (Compound Pulley): Description: A combination of multiple fixed and movable pulleys arranged together to significantly increase the mechanical advantage. It consists of one or more pulleys in a "block" that is fixed, and one or more pulleys in another "block" that is movable (attached to the load).
Function: Provides a very high mechanical advantage, making it possible to lift very heavy loads with relatively little effort. The mechanical advantage is equal to the number of rope segments supporting the movable block. Nigerian
Examples: Used in larger construction cranes to lift heavy beams or machinery. In industrial settings, for lifting heavy components or machinery. * On fishing trawlers or cargo of one or more pulleys in a "block" that is fixed, and one or more pulleys in another "block" that is movable (attached to the load).
Function: Provides a very high mechanical advantage, making it possible to lift very heavy loads with relatively little effort. The mechanical advantage is equal to the number of rope segments supporting the movable block. Nigerian
Examples: Used in larger construction cranes to lift heavy beams or machinery. In industrial settings, for lifting heavy components or machinery. On fishing trawlers or cargo ships for hoisting nets or cargo.
E. Advantages of Using Pulleys: Reduces Effort: Makes it easier to lift heavy objects.
Changes Direction of Force: Allows for more convenient and safer pulling actions (e.g., pulling down instead of lifting up).
Increases Efficiency: Helps in moving loads that would otherwise be impossible for human strength alone.
F. Disadvantages of Using Pulleys: Friction: Friction between the rope and the pulley wheel, and within the axle, reduces efficiency.
Complexity: Systems with multiple pulleys (block and tackle) can be complex to set up. * Bulkiness: Multiple pulleys and long ropes can be cumbersome.
A. Introduction (10 minutes)
Engage with Real-World Scenario: The teacher initiates a discussion by asking students how people lift heavy objects like a bucket of water from a deep well, or how a flag is raised to the top of a pole.
Elicit Prior Knowledge: Ask students if they have seen any machines that use wheels and ropes to lift things. Introduce the term "pulley." Visual Aid/Actual Object: If available, display a picture of a well with a pulley, a flagpole, or a simple pulley model.
B. Presentation and Explanation (20 minutes)
Define Pulley: The teacher explains what a pulley is, using clear and simple language.
Identify Parts: Using diagrams (on the board or chart) or a physical model, the teacher points out and names the parts of a simple pulley (wheel/sheave, axle, rope).
Explain How it Works: Briefly explain the concept of effort, load, and how a pulley helps to make work easier.
Introduce Types of Pulleys: Fixed Pulley: Explain its characteristics (fixed position, changes direction of force, MA=1). Provide Nigerian examples (flagpole, well).
Movable Pulley: Explain its characteristics (moves with load, reduces effort, MA=2). Provide Nigerian examples (construction lifting, mechanics).
Block and Tackle (briefly): Mention that combining pulleys creates more powerful systems for very heavy loads.
Advantages/Disadvantages: Discuss the benefits and drawbacks of using pulleys.
C. Practical Activity: Making and Using Pulleys (40 minutes)
Materials: The teacher should prepare or guide students to gather materials: Strong string or thin rope (approx. 2-3 meters per group) Empty cotton reels or small bicycle wheel rims (as pulley wheels) Strong sticks or dowel rods (as axles, e.g., broomstick handle) Sturdy support (e.g., a table leg, broomstick held by two students, door frame) Various weights (e.g., small bags of sand, textbooks, water bottles, small stones in a bag) Hooks or loops (made from wire if needed)
Group Formation: Divide students into small groups (3-4 students per group).
Constructing a Fixed Pulley: Guide each group to insert the stick (axle) through the center of the cotton reel (wheel). Secure the stick horizontally to a fixed support (e.g., tie it to a table leg, or have two students hold the ends of the stick firmly). Thread the rope over the groove of the cotton reel. Attach a weight (load) to one end of the rope and pull the other end (effort).
Demonstration: Have students observe how pulling down on the rope lifts the load upwards. Discuss that the direction of force has changed. Constructing a Movable Pulley (Optional/Demonstration): This can be more challenging for students to construct independently but is valuable as a teacher demonstration. Tie one end of the rope to a fixed support. Pass the rope under a cotton reel. Attach the load to the axle of this cotton reel. Pull the free end of the rope upwards.
Demonstration: Observe how the pulley moves with the load and how it feels easier to lift (requires less effort).
Experimentation: Students take turns using their constructed pulleys to lift different weights. They should describe what they observe (direction of movement, perceived effort).
Safety: Remind students to handle materials carefully, avoid standing directly under lifting loads, and not to use excessively heavy objects.
D. Group Discussion and Q&A (10 minutes)
Sharing Observations: Each group shares their experience, explaining how their pulley worked and what they observed about the effort required and the direction of force.
Application Brainstorm: Students brainstorm other places in Nigeria where they might see pulleys being used, beyond the examples given.
Instruction to Teacher: Present these questions orally or write them on the board. Allow students to discuss in groups or individually, then review the solutions collaboratively.
Question 1: Look at the diagram of a simple pulley below (Teacher to draw a simple fixed pulley on the board or use a chart).
Identify the following parts: a) The wheel b) The rope c)
The axle d)
The load Solution 1: a) The circular disc with a groove. b) The string/cord passing over the wheel. c) The rod through the center of the wheel, holding it in place. d) The object being lifted (e.g., the bucket tied to the rope).
Commentary: This checks objective 1 (recognize and identify parts of a pulley).
Question 2: Give two common uses of a fixed pulley that you might see in your school or community.
Solution 2: a) Raising the flag on the flagpole at school. b) Lifting water from a well in a village or community. c) (Accept other valid answers like window blinds with a cord).
Commentary: This targets objective 2 (identify and describe uses of pulleys).
Question 3: Explain the main difference between a fixed pulley and a movable pulley.
Solution 3: A fixed pulley is stationary; its wheel does not move up or down with the load. Its main purpose is to change the direction of the force. A movable pulley moves along with the load. Its main purpose is to reduce the effort needed to lift the load (it provides mechanical advantage).
Commentary: This directly assesses objective 3 (distinguish between fixed and movable pulleys).
Question 4: Imagine you want to lift a very heavy bag of cement from the ground to the first floor of a building. Which type of pulley would be most helpful to reduce the effort you need, and why?
Solution 4: A movable pulley (or a block and tackle system, which includes movable pulleys) would be most helpful.
Why: A movable pulley helps to reduce the effort required to lift the heavy load because it provides a mechanical advantage, effectively making the load feel lighter. A fixed pulley would only change the direction, not reduce the effort.
Commentary: This applies objectives 2 and 3 to a practical Nigerian context.
Question 5: Describe the steps you would take to make a simple fixed pulley using a cotton reel, a stick, and a piece of rope.
Solution 5: Insert the stick (axle) through the center hole of the cotton reel (wheel). Secure the stick firmly to a fixed support (e.g., tie it to a table leg or hold it steadily). Thread the rope over the grooved rim of the cotton reel. Attach the load to one end of the rope and apply effort to the other end.
Commentary: This assesses objective 4 (make and use pulley machines).
Community Development and Water Access: Pulleys are crucial in many rural Nigerian communities for drawing water from deep wells. Understanding this helps students appreciate how simple machines contribute to basic needs and community well-being, especially where boreholes or piped water are not available.
Construction Industry and Building Sites: In Nigerian cities and towns, pulleys are routinely used on construction sites, from small-scale building projects to large high-rise constructions. Workers use pulley systems to lift bricks, cement bags, timber, and other heavy materials to higher floors, demonstrating efficiency and safety in manual labor. This connects the lesson to the local economy and urban development. Vehicle Maintenance and Repair (Mechanics' Workshops): Mechanics across Nigeria frequently employ pulley systems (often as part of chain hoists or lifting cranes) to lift heavy car engines, gearboxes, or other vehicle components for repair or replacement. This illustrates how pulleys are essential tools in technical and vocational fields, potentially inspiring future career paths.
Maritime and Fishing Activities: In coastal and riverine communities, pulleys are used on fishing boats to haul nets, or on larger vessels for hoisting sails, anchors, or cargo. This demonstrates the application of pulleys in transport and the fishing industry, highlighting their importance in local livelihoods.