Simple Machines

Grade 7 · General Science

Semester 1 | Period 3 | Week 16

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Subject: General Science

Semester: 1

Period: 3

Week: 16

School Name:
Teacher’s Name:
Subject: General Science
Grade Level: Grade 7
Date:
Week 16 Lesson Duration: 45 minutes
Week & Period: Week 16, Period 3
Topic: Simple Machines
Sub-topic: Wheel & Axle, Pulley, Wedge

Learning Objectives
By the end of the lesson, students should be able to:

  1. Identify and describe the structure and function of wheel & axle, pulley, and wedge.
  2. Explain how these simple machines make work easier.
  3. Give examples of wheel & axle, pulley, and wedge in daily life and in Liberia.

Previous Knowledge
Students already know:
• Definition and purpose of simple machines
• Levers, inclined planes, and screws as simple machines

Instructional Materials
• Textbook: General science textbooks for Grade 7
• Teaching aids: Models of wheel & axle, pulley, wedge, charts showing practical examples
• 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 machines or tools that help you move heavy objects or cut things easily?
• Have you used a water wheel, a flag pulley, or an axe before? How did they help?
The teacher will record their responses on the board.
Teacher’s Role: Guide brainstorming, clarify misconceptions, and link ideas to simple machines.
Learner’s Role:
• Share examples of wheel & axle, pulleys, and wedges they have seen or used.
• Participate in discussion and respond verbally.

B – Building Knowledge (Main Lesson Body)

Time: 25–30 minutes

Teacher’s Role (Expanded & Detailed)

  1. Introduce Wheel & Axle
    • Definition: A wheel and axle is a simple machine made of a large wheel attached to a smaller rod (axle). When the wheel turns, the axle turns too.
    • Principle: It reduces effort needed to move or carry loads by increasing speed or force.
    • Examples: carts, bicycles, doorknobs, car steering wheels.
    • Local Liberian Examples:
      • Pushcarts used in markets to move heavy goods.
      • Bicycles used in rural communities for transport.
      • Grinding mills for palm fruits or cassava.
    • Demonstration: Show how turning a toy car wheel or a doorknob requires less effort than turning the axle alone.
  2. Explain Pulley
    • Definition: A pulley is a wheel with a rope, chain, or belt over it that helps lift or move heavy objects by changing the direction of force.
    • Types:
      • Fixed Pulley: Changes the direction of force only (e.g., flagpole).
      • Movable Pulley: Reduces the effort needed to lift (e.g., construction crane, well pulley).
      • Combination (Block and Tackle): Uses several pulleys together to make lifting very heavy loads easier.
    • Local Liberian Examples:
      • Water wells in rural villages.
      • Raising the Liberian flag on a flagpole at school.
      • Pulleys used in construction to lift cement blocks.
    • Demonstration: Tie a rope over a wheel or bottle top, use it to lift a stone—compare effort with and without pulley.
  3. Explain Wedge
    • Definition: A wedge is a triangular or pointed tool that cuts, splits, or lifts objects by applying force over a larger area.
    • Principle: Converts a force applied on a wide surface into a concentrated force at a narrow edge.
    • Examples: axe, knife, chisel, doorstop, nail.
    • Local Liberian Examples:
      • Axe for splitting firewood.
      • Cutlass for farming and clearing bushes.
      • Knife for cooking in homes.
      • Wooden wedges used to hold doors open.
    • Demonstration: Use a knife to cut fruit, or show how an axe splits wood with less effort.
  4. Relating to Daily Life in Liberia
    • Wheel & Axle: used for transportation (motorbikes, wheelbarrows).
    • Pulley: used to fetch water, raise loads in construction.
    • Wedge: used in farming, carpentry, cooking, and logging.
    • Stress: These machines reduce effort, save time, and make heavy tasks manageable.

 

Learners’ Activities (Expanded & Interactive)

  • Observation: Watch demonstrations of wheel & axle (toy car), pulley (rope lifting object), wedge (cutting fruit).
  • Hands-on Practice:
    • Students roll a ball or push a cart to feel how wheels reduce effort.
    • Students try pulling a stone with and without a pulley to compare effort.
    • Students cut soft fruit (e.g., banana) with a knife to see wedge action.
  • Identification Task: Walk around class or school compound to identify tools (wheelbarrow = wheel & axle, rope on flagpole = pulley, cutlass = wedge).
  • Discussion in Pairs: How would life be harder without these machines?

 

Assessment Checks (Expanded & Varied)

  1. Oral Questions:
    • What is the main function of a wheel and axle?
    • Give one local example of a pulley in Liberia.
    • Why is an axe a wedge?
  2. Quick Written Quiz (in notebooks):
    • A bicycle works with which simple machine?
      A) Lever
      B) Wheel & axle
      C) Pulley
      D) Wedge
    • Which type of pulley only changes the direction of force but not the effort?
      A) Fixed pulley
      B) Movable pulley
      C) Block and tackle
      D) Wheel & axle
    • Which tool is an example of a wedge?
      A) Screw
      B) Pulley
      C) Knife
      D) Wheelbarrow
  3. Practical Check:
    • Teacher holds an axe: “What simple machine is this and why?”
    • Teacher shows a wheelbarrow: “Which part is the wheel & axle?”
  4. Application Question:
    • “Imagine you are a builder in Monrovia who must lift heavy cement blocks. Which simple machine would you choose and why?”

Notes (Expanded & Detailed)

  • Wheel & Axle: Makes it easier to move or carry loads; examples include bicycles, cars, wheelbarrows.
  • Pulley: Lifts heavy objects and changes direction of force; can be fixed, movable, or block & tackle.
  • Wedge: Splits, cuts, or lifts objects; examples include knives, axes, cutlasses.
  • Key Principle: All these machines don’t reduce total work done but make it easier and safer by reducing effort or changing force direction.
  • Practical Importance in Liberia:
    • Transportation: wheel & axle in cars, motorbikes.
    • Construction: pulleys to lift building materials.
    • Farming & domestic life: wedges in cutlasses, axes, knives.
  • Safety Emphasis: Always use simple machines correctly (e.g., handle knives carefully, secure ropes in pulleys, maintain bicycle wheels).

 

C – Consolidation (Conclusion & Assessment)
Time: 5–10 minutes
Summary:
• The teacher will ask the students to recall:

  • Structure and function of wheel & axle, pulley, and wedge
  • Examples of each in daily life
  • How these simple machines make work easier
    Evaluation Method (Expanded):
    • Exit slip/quiz: Students will write short answers to:
  1. Give one example of a wheel & axle, a pulley, and a wedge.
  2. Explain how a pulley helps in lifting heavy objects.
  3. State one safety measure when using a wedge.
    Teacher will collect and quickly review for understanding
    • Provide oral feedback before class ends

Assignment (Expanded): Follow-up Activity:
• Identify and list five simple machines (including wheel & axle, pulley, wedge) at home, school, or in the community and describe their use.
• Draw and label one simple machine, explaining how it reduces effort.

Differentiation / Inclusive Strategies
• Struggling Learners: Use step-by-step demonstrations and simple examples.
• Advanced Learners: Investigate compound machines combining wheel & axle, pulleys, and levers.
• Students with Disabilities: Use tactile models, peer support, and visual aids for hands-on learning.

Teacher’s Reflection (After Class)
• What worked well? ______________________________________________________
• What needs improvement? _________________________________________________
• Students’ engagement level: □ High □ Medium □ Low