NCERT Class 9 Science Exploration: Chapter 7 — 7. Work, Energy, and Simple Machines
This chapter introduces the concepts of work, energy, and power, which simplify the analysis of motion and interactions. It explores simple machines that enable tasks with less effort and greater convenience, serving as fundamental components of everyday machinery. Energy, defined as the capacity to do work, is central to these ideas and daily activities. The chapter begins by defining work done by a constant force, explaining that work is the product of the force applied and the displacement in the direction of the force. It illustrates this with examples of lifting objects of varying masses to different heights, demonstrating how work done is proportional to both force and distance. This foundational understanding is crucial for comprehending more complex mechanical systems and energy transformations in physics.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 9 |
| Subject | Science |
| Book | Exploration |
| Chapter | Chapter 7 — 7. Work, Energy, and Simple Machines |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 3 minutes |
| Word count | 564 |
Learning outcomes
- Understand the scientific definitions of work, energy, and power.
- Analyze situations involving constant forces and displacement.
- Recognize the relationship between force, displacement, and work done.
- Identify simple machines as tools that reduce effort.
- Appreciate the role of energy in daily activities and physical processes.
Vocabulary
| Word | Meaning |
|---|---|
| Force | An influence that can change the motion of an object. |
| Motion | The process of moving or being moved. |
| Kinematic equations | Equations that describe motion without considering its causes. |
| Newton's laws | Fundamental laws of motion and gravity. |
| Work | The energy transferred when a force moves an object over a distance. |
| Energy | The capacity to do work. |
| Power | The rate at which work is done or energy is transferred. |
| Simple machines | Basic mechanical devices that change the direction or magnitude of a force. |
| Displacement | The change in position of an object. |
| Constant force | A force that does not change in magnitude or direction. |
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Practice questions
- Define work done by a constant force. Answer: Work done by a constant force is defined as the product of the force applied and the displacement in the direction of the force.
- What is the scientific definition of energy? Answer: Energy is the capacity to do work.
- If you apply a force of 10 N and displace an object by 5 m in the direction of the force, how much work is done? Answer: Work done = Force × Displacement = 10 N × 5 m = 50 Joules.
- What is the difference between everyday language and scientific definition of 'work'? Answer: In everyday language, 'work' can refer to any strenuous activity. Scientifically, work is done only when a force causes a displacement.
Frequently asked questions
What is the main focus of Chapter 7 of NCERT Class 9 Science?
Chapter 7 focuses on Simple Machines, along with the fundamental concepts of work, energy, and power.
How is work defined scientifically?
Scientifically, work is defined as the product of the force applied to an object and the displacement of the object in the direction of the force.
What is energy according to the chapter?
Energy is defined as the capacity to do work.
What are simple machines?
Simple machines are basic mechanical devices that help us perform tasks with less effort and more convenience.
Does applying a larger force over the same distance mean more work is done?
Yes, according to the chapter, applying a larger force over the same distance proportionally results in more work done.
What is the relationship between force and displacement in the definition of work?
Work is done when a force causes a displacement, and the work done is calculated by multiplying the force by the displacement in the direction of the force.
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Topics covered
NCERT Class 9 Science — Exploration — Chapter 7 — 7. Work, Energy, and Simple Machines. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.