Force, Work, and Power

Grade 7 · General Science

Semester 1 | Period 3 | Week 17

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Subject: General Science

Semester: 1

Period: 3

Week: 17

School Name:
Teacher’s Name:
Subject: General Science
Grade Level: Grade 7
Date:
Week 17 Lesson Duration: 45 minutes
Week & Period: Week 17, Period 3
Topic: Force, Work, and Power
Sub-topic: Definitions, Relationship with Energy, Solving Simple Problems

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

  1. Define force, work, and power in scientific terms.
  2. Explain the relationship between force, work, power, and energy.
  3. Solve simple numerical problems involving force, work, and power using appropriate formulas.

Previous Knowledge
Students already know:
• Basic concepts of energy, potential and kinetic energy
• Simple machines and how they make work easier

Instructional Materials
• Textbook: General science textbooks for Grade 7
• Teaching aids: Spring balance, weights, rulers, charts showing force, work, and power relationships
• 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:
• Have you ever pushed or lifted an object? How would you describe the effort you used?
• Can all efforts you make be considered “work” in science? Why or why not?
The teacher will record their responses on the board.
Teacher’s Role: Guide brainstorming, clarify misconceptions, and link everyday experiences to scientific concepts.
Learner’s Role:
• Share experiences of lifting, pushing, or moving objects.
• Respond verbally and participate in discussion.

B – Building Knowledge (Main Lesson Body)

Time: 25–30 minutes

Teacher’s Role (Expanded & Detailed)

  1. Introduce Force
    • Definition: Force is a push or a pull that can change the state of motion or shape of an object.
    • Types of force:
      • Muscular force (pushing a wheelbarrow).
      • Gravitational force (fruit falling from a tree).
      • Frictional force (a bicycle slowing down on the road).
    • SI Unit: Newton (N).
    • Local Examples in Liberia:
      • Farmers pushing carts of cassava.
      • A student pulling open the school door.
      • Motorbike tires gripping the road due to friction.
    • Demonstration: Push a chair → explain force in action.
  2. Explain Work
    • Definition: Work is done when a force is applied on an object and the object moves in the direction of the force.
    • Formula:

Work=Force×Distance

  • SI Unit: Joule (J).
  • Key point: If the object does not move, no work is done even if force is applied.
  • Local Examples:
    • Carrying a bucket of water upstairs (work is done because the bucket moves upward against gravity).
    • A mason lifting cement blocks onto scaffolding.
    • A farmer pushing a wheelbarrow full of vegetables to the market.
  • Demonstration: Lift a 2-liter water container and walk a short distance → calculate work done.
  1. Explain Power
    • Definition: Power is the rate at which work is done.
    • Formula:

Power=      Work

     Time

  • SI Unit: Watt (W).
  • Key point: If two people do the same work but one finishes faster, that person has greater power.
  • Local Examples:
    • Two students fetching water: one fills the same number of buckets in half the time → more powerful.
    • A generator producing electricity faster than manual work.
    • A car reaching Ganta faster than a motorbike, though both cover the same distance.
  • Demonstration: Time two students lifting books from the floor to a desk, compare their power.
  1. Relationship between Force, Work, Power, and Energy
    • Energy: the capacity to do work.
    • Work: the transfer of energy (e.g., lifting water transfers muscular energy to gravitational potential energy).
    • Power: how quickly the work is done (energy transferred per unit time).
    • Simple Flow:
      Energy → enables Force → does Work → rate of Work = Power.
  2. Problem Solving (Teacher-led, then student practice)
    • Example 1 (Work):
      A student pushes a box with a force of 20 N for 5 m.
      Work = 20 × 5 = 100 J.
    • Example 2 (Power):
      If the student takes 10 seconds,
      Power = 100 ÷ 10 = 10 W.
    • Local Example:
      Lifting a bucket of water (15 N) up a well (4 m deep).
      Work = 15 × 4 = 60 J.
      If it takes 6 seconds: Power = 60 ÷ 6 = 10 W.

 

Learners’ Activities (Expanded & Interactive)

  • Observation: Watch teacher’s force, work, and power demonstrations.
  • Hands-On Activities:
    • In small groups, push chairs/tables across the room → calculate work done.
    • Use a stopwatch to time how fast classmates can lift objects → calculate power.
    • Discuss why “pushing a wall” is not work (no displacement).
  • Discussion Questions:
    • “What happens to work done if we double the force but keep distance the same?”
    • “If two people carry the same load but one is faster, who has more power?”
  • Local Application Task: Students brainstorm how force, work, and power apply to farming, construction, and transportation in Liberia.

 

Assessment Checks (Expanded & Varied)

  1. Oral Questions:
    • Define force, work, and power in your own words.
    • Give one Liberian example of work and one example of power.
    • Why is no work done if an object does not move?
  2. Quick Written Problems:
    • A farmer uses a force of 50 N to push a wheelbarrow 10 m. Calculate the work done.
    • A mason lifts a 200 N block 2 m high in 5 seconds. Calculate the power.
  3. Group Challenge:
    • Group A and Group B both lift identical buckets of water. Group A does it in 15 seconds, Group B in 10 seconds. Who is more powerful and why?
  4. Concept Application:
    • Teacher asks: “When you ride a bicycle uphill, are you doing work? Why?”
    • “How is energy linked to the work you are doing?”

 

Notes (Expanded & Detailed)

  • Key Definitions:
    • Force = push or pull (Newton).
    • Work = Force × Distance (Joule).
    • Power = Work ÷ Time (Watt).
  • Relationships:
    • Doing work transfers energy.
    • Power measures how quickly work is done.
  • SI Units:
    • Force → Newton (N).
    • Work → Joule (J).
    • Power → Watt (W).
  • Real-Life Importance in Liberia:
    • Construction: lifting cement, building bridges, using cranes.
    • Transportation: motorbikes use more power than bicycles.
    • Domestic life: drawing water from a well, carrying loads to market.
  • Practical Tip: Efficiency matters – using tools (like levers and pulleys) reduces the force needed, saving human energy.

 

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

  • Definitions of force, work, and power
  • Relationship between work, energy, and power
  • How to solve simple problems involving work and power
    Evaluation Method (Expanded):
    • Exit slip/quiz: Students will write short answers to:
  1. Define work and give an example from daily life.
  2. State the formula for power and explain it.
  3. Solve: A force of 20 N moves a box 5 m. Calculate the work done.
    Teacher will collect and quickly review for understanding
    • Provide oral feedback before class ends

Assignment (Expanded): Follow-up Activity:
• Identify three examples of work done at home or school and calculate the work using approximate force and distance.
• Write a paragraph explaining how power can be increased while doing work.

Differentiation / Inclusive Strategies
• Struggling Learners: Provide step-by-step worked examples and guided practice.
• Advanced Learners: Solve more complex problems combining multiple forces or time intervals.
• Students with Disabilities: Use tactile measuring tools, peer support, and visual aids for demonstrations.

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