Machines and Work

Grade 8 · General Science

Semester 1 | Period 3 | Week 17

Download the Lessonotes Mobile Liberia app for faster lesson access on Android and iPhone.

Get it on Google Play Get it on the Apple App Store

Subject: General Science

Semester: 1

Period: 3

Week: 17

School Name:
Teacher’s Name:
Subject: General Science
Grade Level: Grade 8
Date: Week 17
Lesson Duration: 45 minutes
Week & Period: Week 17, Period 3
Topic: Machines and Work
Sub-topic: Learning Objectives
By the end of the lesson, students should be able to:

  1. Identify the types of simple machines.
  2. Explain how work is done using simple machines.
  3. Solve basic problems involving work and relate machines to daily life activities.

Previous Knowledge
Students already know:
• Forms of energy (mechanical, heat, light)
• Forces (gravity, friction, cohesion, adhesion)
Instructional Materials
• Textbook: General Science textbooks for Grade 8
• Teaching aids: models of lever, pulley, inclined plane, wheel and axle, wedge, screw; spring balance; weights
• Students' notebooks and writing materials
Lesson Development – ABC Model
A – Anticipation (Warm-up / Starter)
Time: 5–10 minutes
Activity: The teacher will ask the class:
• Can you think of ways to lift heavy objects easily at home or school?
• Have you seen pulleys or levers in use locally?
The teacher will record responses on the board.
Teacher’s Role: Guide brainstorming and link responses to the concept of machines.
Learner’s Role:
• Share personal experiences of using simple tools or machines.
• Participate actively in discussion.
B – Building Knowledge (Main Lesson Body)

Time: 25–30 minutes

Teacher’s Role (Expanded & Detailed)

  1. Explain Types of Simple Machines with Local Examples
  • Lever
    • A rigid bar that pivots on a fulcrum to move a load using less effort.
    • Examples: seesaws in schools, crowbars for lifting stones, wooden planks used in small construction sites.
    • Local relevance: Farmers lifting water buckets from wells using lever-type devices.
  • Pulley
    • A wheel with a rope that changes the direction of a force to lift a load.
    • Examples: lifting water from wells, hoisting flagpoles.
    • Local relevance: Water wells in Monrovia and rural Liberia; flagpoles in schools and government buildings.
  • Inclined Plane
    • A flat surface sloped at an angle to raise or lower objects with less effort.
    • Examples: ramps, sloped roads.
    • Local relevance: Loading goods onto trucks, access ramps for buildings.
  • Wheel and Axle
    • A large wheel attached to a smaller axle; force applied to wheel moves load efficiently.
    • Examples: bicycles, carts, water wheels.
    • Local relevance: Bicycle transport, wheelbarrows in farms or markets.
  • Wedge
    • A piece of material with a sharp edge to split or cut objects.
    • Examples: knives, axes, machetes.
    • Local relevance: Cutting wood, cassava processing, cooking preparation.
  • Screw
    • A spiral inclined plane; converts rotational motion into linear motion.
    • Examples: bottle caps, screws in carpentry.
    • Local relevance: Furniture making, bottle sealing, constructing doors and windows.

 

  1. Introduce Concept of Work
  • Definition: Work is done when a force moves an object over a distance.
  • Formula: Work (W) = Force (F) × Distance (d)
    • Force in Newtons (N), Distance in meters (m), Work in Joules (J).
  • Examples:
    • Lifting a water bucket from a well.
    • Pushing a cart of goods along a flat surface.
  • Discuss energy efficiency: Simple machines reduce effort but work done equals the load × distance (ignoring friction).

 

  1. Discuss Real-Life Applications
  • Lifting heavy objects (lever, pulley).
  • Transporting goods on ramps, carts, or wheelbarrows (inclined plane, wheel and axle).
  • Cutting and processing food or wood (wedge).
  • Constructing objects with screws (screw).
  • Emphasize local Liberian context: schools, markets, farms, construction sites.

 

Learners’ Activities (Expanded & Practical)

  1. Identification Activity
  • Learners identify simple machines in classroom, school compound, or community.
  • Draw diagrams and label type, load, effort, and fulcrum (for levers).
  1. Group Work: Calculation of Work Done
  • Solve simple numerical problems using W = F × d.
  • Example: Force = 20 N, Distance = 5 m → Work = 20 × 5 = 100 J.
  • Assign more problems with varying force and distance.
  1. Practical Demonstrations
  • Teacher demonstrates lifting a bucket using a lever or pulley.
  • Learners measure force and distance and calculate work done.

 

Assessment Checks (Expanded)

  • Oral Questions:
    • Which simple machine is used to raise water from a well? (Pulley)
    • Give one local example of a wedge. (Knife, axe, machete)
  • Written Exercise:
    • Solve: A force of 50 N moves a crate 3 m. Calculate work done. (W = 50 × 3 = 150 J)
    • Identify the simple machine used in a bicycle wheel, a bottle cap, and a ramp.
  • Practical Check:
    • Observe learners lifting or moving objects with classroom materials and calculate work done.

 

Notes (Expanded & Detailed)

  • Simple Machines: Devices that make work easier by changing force magnitude or direction.
  • Levers: Can increase force or distance; classified as first, second, third class.
  • Pulleys: Single pulleys change direction; multiple pulleys reduce effort.
  • Inclined Planes: Reduce force needed but increase distance traveled.
  • Wheel and Axle: Converts small force on the wheel to greater force on axle.
  • Wedges and Screws: Transform force for cutting or lifting.
  • Work: Work done depends on force applied and distance moved; measured in Joules (J).
  • Efficiency: Some energy lost to friction; simple machines reduce effort but cannot eliminate work.
  • Local relevance: lifting water, transporting goods, construction, cutting, and assembly tasks.

 

Extended Assignment

  1. Identify five simple machines in your community and describe their use.
  2. Solve five numerical problems on work done using W = F × d.
  3. Draw and label a lever system showing load, effort, and fulcrum.
  4. Write a short paragraph on how simple machines reduce effort in daily life in Liberia.


C – Consolidation (Conclusion & Assessment)
Time: 5–10 minutes
Summary:
• Teacher asks students to recall types of simple machines and the formula for work.
Evaluation Method (Expanded):
• Exit slip/quiz: Students write:

List three types of simple machines and one local example each.

Calculate the work done when a force of 15 N moves an object 3 m.
• Teacher collects and provides feedback.
Assignment (Expanded):
• Identify simple machines used in your household and describe their use.
• Prepare two practical examples demonstrating how work is done using a simple machine.
Follow-up Activity:
• Demonstrate one simple machine (e.g., lever or pulley) next lesson and measure work done.
Differentiation / Inclusive Strategies
• Struggling Learners: Focus on identifying simple machines using pictures and classroom objects.
• Advanced Learners: Solve multi-step problems involving work and mechanical advantage.
• Students with Disabilities: Use hands-on models, peer assistance, and visual cues for explanation.
Teacher’s Reflection (After Class)
• What worked well? ______________________________________________________
• What needs improvement? _________________________________________________
• Students’ engagement level: □ High □ Medium □ Low