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New NCERT textbook · Class 9 Science

Exploration, period by period — fitted to your timetable.

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Chapter 7 · Period 1 of 22 · 50 min

Calculating Work Done When Force Moves an Object

7.1 Work Done by a Constant Force · Didactic approach

This unit is the chapter's entry point into the scientific meaning of work, so it is worth spending a moment letting students surface their everyday sense of 'effort' before introducing the formal definition — the contrast will pay off in the next section on zero work. Watch for students who confuse force alone with work; the wheat-bag comparison is specifically designed to show that displacement is equally essential. A useful checkpoint: students should be able to state why pushing a stationary wall involves no work before you move on.

0-8Open with the wheat-bag scenario from the chapter: ask students to compare lifting one bag 2 m versus two bags 1 m and predict which takes more effort, then poll for reasoning. Record responses on the board without evaluating.
8-25Develop the formal definition W = F × s, tracing how both force and displacement independently scale the work done, using the wheat-bag numbers as a running example. Introduce the joule as the SI unit and work through a brief numerical: a 10 N force over 3 m.
25-38Draw and interpret the force-displacement graph: show a constant-force rectangle and establish that area = work. Pose a varying-force graph (stepped or trapezoidal) and ask pairs to estimate the total work by counting approximate areas, then compare answers.
38-50Students individually write the formal definition in their own words, sketch a force-displacement graph for a 5 N force over 4 m, label the axes, shade the area, and calculate the work. Pairs exchange and check each other's shading and calculation.
Assessment

Competency (C-2.5). Defines work in scientific terms and represents the relationship between potential and kinetic energy in mathematical expressions.

Learning outcome. Students can calculate the work done by a constant force using the product of force and displacement and represent this on a force-displacement graph.

A force-displacement graph for an object shows a horizontal line at 8 N from a displacement of 0 m to 3 m, and then drops to 0 N. What is the total work done on the object?

  • A 3 J
  • B 8 J
  • C 11 J
  • D 24 J

D. 24 J

What each wrong option reveals

  • A Reads only the displacement value (3 m) without multiplying by force — confuses displacement with work.
  • B Reads only the force value (8 N) without multiplying by displacement — confuses force with work.
  • C Adds force and displacement (8 + 3 = 11) instead of multiplying — treats work as a sum rather than a product.
Chapter 7 · 22 periods of 50 min

Also saved as 13 periods or 18 periods.

  • 2Identifying Conditions Where Scientific Work Equals Zero
    7.1.1 When is work done equal to zero?
  • 3Determining the Sign of Work Done in Opposing-Force Situations
    7.1.2 Positive and negative work done
  • 4Applying the Work-Energy Theorem to Track Energy Transfers
    7.2 The Work-Energy Theorem
  • 5Classifying and Converting Between Forms of Energy
    7.3 Forms of Energy
  • 6Deriving Kinetic Energy from Newton's Second Law and Kinematics
    7.4.1 Kinetic energy
  • 7Exploring How Positive and Negative Work Changes Kinetic Energy
    7.4.1 Kinetic energy
  • 8Investigating Stored Energy in Deformed Objects and Position
    7.4.2 Potential energy
  • 9Deriving Gravitational Potential Energy Using the Work-Energy Theorem
    7.4.2 Potential energy
  • 10Proving Conservation of Mechanical Energy with a Pendulum
    7.4.3 Conservation of mechanical energy
  • 11Solving Conservation-of-Mechanical-Energy Problems in Novel Contexts
    7.4.3 Conservation of mechanical energy
  • 12Defining Power and Calculating the Rate of Doing Work
    7.5 Power
  • 13Introducing Simple Machines: Effort, Load, and Mechanical Advantage
    7.6 Simple Machines
  • 14Analysing Fixed and Movable Pulleys and Their Mechanical Advantages
    7.6.1 Pulley
  • 15Measuring How Incline Angle Affects the Effort Needed to Raise a Load
    7.6.2 Inclined plane
  • 16Discovering the Lever Principle Through a Ruler-and-Pencil Investigation
    7.6.3 Lever
  • 17Building a Beam Balance and Classifying Lever Types by Fulcrum Position
    7.6.3 Lever
  • 18Tracing Energy Transformation in the Gharat and Hydroelectric Systems
    7.6.3 Lever
  • 19Connecting Mechanical Advantage Across All Three Simple Machines
    7.6.3 Lever
  • 20Applying W = F × s and KE = ½mv² to Multi-Step Problem Sets
    7.4.1 Kinetic energy (Revisit)
  • 21Reasoning About Energy Conservation and Mechanical Advantage in New Scenarios
    7.4.3 Conservation of mechanical energy (Revisit)
  • 22Whole-Chapter Synthesis: Connecting Work, Energy, and Simple Machines
    Synthesis
Exploration · Class 9 · 13 chapters

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