Table of Contents
Class 9 Notes Science Chapter 11: In Class 9, Chapter 11 called ‘Work and Energy’ talks about work, energy, and power in detail. In everyday language, we often equate any productive physical or mental exertion with work. However, in scientific terms, work carries a specific definition. It occurs when a force is applied to an object, causing it to move. The amount of work done is calculated by multiplying the force exerted by the distance the object moves in the direction of the force. Unlike some other physical quantities, work is scalar, meaning it has magnitude but not direction.
Also Check: Work, Power And Energy Class 9 Extra Questions
What is Work?
Work is achieved when an object is pushed or pulled, causing it to move in the direction of the force applied. To determine the amount of work done, multiply the magnitude of the force (the strength of the push or pull) by the distance the object moves in that direction (the displacement). It’s written as W = F.s. The force is measured in Newtons.
If you apply force to an object but it remains stationary, no work is accomplished. For example, if you try to push a wall and it doesn’t budge.
When exerting a push or pull at an angle on an object, only a component of that force contributes to its movement. This component can be determined by multiplying the force by the cosine of the angle between the force and the direction in which the object is moving.
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Download Class 9 Science Revision Notes Chapter 11 2024-25 PDF
CBSE Class 9 Science revision notes of Chapter 11 are prepared to assist students in preparing for their exams. These notes have been meticulously prepared by subject matter experts in accordance with the CBSE syllabus. Our aim is to provide students with comprehensive and concise study material that covers all essential topics, making their exam preparation efficient and effective. With these notes at their disposal, students can enhance their understanding of key concepts and boost their confidence for the upcoming examinations.
Download Free PDF of CBSE Class 9 Chapter 11 Revision Notes | |
What is Work (Introduction) | What is Work (Formulas) |
What is Energy | Mechanical Energy |
Kinetic Energy | Kinetic Energy (Word Problems) |
Potential Energy | Law of Conservation of Energy |
What is Power |
CBSE Class 9 Notes Science Chapter 11 – Important Concepts
Facts that Matter
Work is defined as the product of a force acting on an object and the displacement of that object in the direction of the force. Two conditions must be met for work to occur:
- A force must be exerted on the object.
- The object must undergo displacement.
The formula to calculate work is:
Work = Force × Displacement
The unit of work is the Joule, which is equivalent to the product of a Newton (the unit of force) and a meter (the unit of displacement).
Thus, 1 Joule of work is said to be done when a force of 1 Newton is applied to an object and it undergoes displacement by 1 meter..
Energy
The ability of a body to perform work is referred to as its energy.
Unit of energy = Joules 1KJ = 1000 J
There are several distinct forms of energy, including potential energy, kinetic energy, heat energy, chemical energy, electrical energy, and light energy.
Kinetic energy is the energy that an object possesses due to its motion. The kinetic energy of an object is directly proportional to its velocity, meaning that as the object’s speed increases, so does its kinetic energy. This kinetic energy can be quantified by considering the work done to impart the object with its specific velocity.
Derivation
Consider an object of mass 𝑚 moving with a uniform velocity 𝑢 Let’s displace it by a distance 𝑠 due to a constant force 𝐹 acting on it.
Potential Energy
The energy that a body holds as a result of its position or configuration is termed its potential energy
shape
Don’t Miss:
Chapter-Wise NCERT Solutions for Class 9 Science
- Chapter 1 Matter in Our Surroundings
- Chapter 2 Is Matter Around Us Pure
- Chapter 3 Atoms and Molecules
- Chapter 4 Structure of The Atom
- Chapter 5 The Fundamental Unit of Life
- Chapter 6 Tissues
- Chapter 7 Diversity in Living Organisms
- Chapter 8 Motion
- Chapter 9 Force and Laws of Motion
- Chapter 10 Gravitation
- Chapter 11 Work and Energy
- Chapter 12 Sound
- Chapter 13 Why Do We Fall ill
- Chapter 14 Natural Resources
- Chapter 15 Improvement in Food Resources
Gravitational Potential Energy: (GP)
When an object is lifted to a certain height, energy is expended to overcome gravity, resulting in what we call gravitational potential energy. This potential energy is calculated by considering the work done in lifting the object from the ground to its final position against the force of gravity.
Derivation
When considering a body of mass 𝑚 being raised through a height ℎ from the ground, the force required to lift the object is equal to the weight of the object, 𝑚𝑔
mg. As the object is lifted, it gains energy due to the work done on it.
The work done in both cases (i) and (ii) remains the same when a body is raised from position A to B, regardless of the path taken, as long as the height attained is consistent.
Mechanical Energy refers to the combined energy of kinetic energy and potential energy.
According to the Law of Conservation of Energy, energy cannot be created or destroyed; it can only change from one form to another. The total energy before and after any transformation remains constant.
Potential energy + Kinetic energy = Constant (Mechanical energy)
When a body of mass ‘m’ is elevated to height ‘h’ at point A, its potential energy is at its maximum while its kinetic energy is zero since it’s stationary. As the body descends to point B, its height ‘h’ decreases, leading to a reduction in potential energy, while its velocity ‘v’ increases, resulting in an increase in kinetic energy. As the body approaches ground level, where height ‘h’ equals zero, its velocity ‘v’ reaches its maximum, thus maximizing kinetic energy while potential energy diminishes.
The decline in potential energy corresponds to the rise in kinetic energy, illustrating the continuous conversion of gravitational potential energy into kinetic energy.
Power
Commercial Unit of Energy
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Law of Conservation of Energy
The principle of conservation of energy states that energy cannot spontaneously emerge from nothing or vanish into nothingness. Rather, it undergoes transformations from one form to another. Throughout these transformations, the total quantity of energy remains constant, unaffected by the changes in its various forms.
Total energy = KE + PE
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Class 9 Notes Science Chapter 11 FAQs
What is work power and energy class 9?
In Physics, there are three important things to know: Work, Energy, and Power. Work happens when you use a force, like a push or pull, to move something. Energy is the ability to do work. And Power is how much work gets done in a certain amount of time.
What is the main formula of work and energy Class 9?
Energy helps us do work. There are different kinds of energy, like kinetic (when something's moving) and potential (when it's ready to move). We can show work as W = F.d, where 'F' is the force used and 'd' is how far something moves.
What is the work and energy theorem Class 9?
The work-energy idea says that all the forces working on something add up to the change in its energy.