Greetings to all today we are going to upload the **Work Power and Energy Class 9 Notes PDF** for the assistance of students as well as teachers. We have given the summary and revision notes for Class 9 Science Chapter 11. This CBSE note contains CBSE Key Notes, CBSE Revision Notes, Short Key Notes, diagrams of the complete Chapter 11 titled Work, Power, And Energy of Science taught in class 9. If you are a student of class 9 who is using the NCERT Textbook to study Science, then you must come across** Chapter 11 Work, Power And Energy.** After you have studied the lesson, you must be looking for notes to memorize. From here you can get complete Chapter 11 Work, Power And Energy class 9 notes in one place. For a better understanding of this chapter, you should also see NCERT Solutions for Class 9 Science Chapter 11 Work, Power, And Energy.

### Detailed Table of the Chapter 11 Notes – Work Power and Energy Class 9 Notes PDF

1. |
Board |
CBSE |

2. |
Textbook |
NCERT |

3. |
Class |
Class 9 |

4. |
Subject |
Science Notes |

5. |
Chapter |
Physics Chapter 11 |

6. |
Chapter Name |
Work, Power, and Energy Class 9 Notes |

7. |
Category |
CBSE Revision Notes |

## Work Power and Energy Class 9 Notes PDF

**Introduction**

For the average person, the term “work” refers to any task that requires bodily or mental effort. However, in physics, the phrase has a different meaning. It denotes a measurable quantity. We say that a force has done work on an object when it acts on it and causes it to move in the direction of the force.

When you push a book on a table, you apply force to the book, which causes it to move in the direction of the force. We say the force has done its job.

You will be exhausted if you push a wall, but the wall will not move. There is no work done in terms of science.

**Work and Measurement of Work**

When a force acts on an object and the point of application moves in the direction of the force, work is said to be completed.

**Conditions to be Satisfied for Work to be Done:**

- There must be some force acting on the object
- The point of application of force must move in the force’s direction
- Work is calculated by multiplying the force by the distance traveled.

W=F × SW=F × S

Where W denotes the amount of work done, F is the force exerted, and S denotes the distance traveled by the moving object. The amount of work completed is a scalar quantity.

3. **Work Done When the Force is not Along the Direction of Motion:**

Assume that a constant force F acts on a body, resulting in a displacement S as illustrated in the diagram. Let θθ be the angle formed by the force and displacement directions.

Displacement in the direction of the force == Component of SS along AXAX =AC=AC

But we know that,

cosθ=cosθ= adjacent side hypotenuse adjacent side hypotenuse

cosθ=ACScosθ=ACS

AC=ScosθAC=Scosθ

Displacement in the direction of the force =Scosθ=Scosθ

Work done ==Force ×× displacement in the direction of force

W=FScosθW=FScosθ

If the displacement SS is in the direction of the force

FS=0,cosθ=1FS=0,cosθ=1

Then,

W=FS×1W=FS×1

W=FSW=FS

If,

θ=90∘θ=90∘

cos90∘=0cos90∘=0

Therefore,

W=F.S×0=0W=F.S×0=0

i.e, no work is done by the force on the body.

**The Centripetal Force is Activated When a Stone at the End of a String is Whirled Around in a Circle at a Constant Speed.**

This force is perpendicular to the stone’s velocity at any given time. So, even though it is responsible for retaining the stone in a circular motion, this force does no work.

## Work Power and Energy Class 9 Notes PDF – Important Points

**SI Unit of Work:**

W=F×SW=F×S

SI unit of FF is NN and that of SS is mm N=newtonN=newton

SI unit of work=N×m=N×m

1Nm1Nm is defined as 11 joules.

i.e., 11 joule =1Nm=1Nm

So, the SI unit of work is Joule.

A joule is the amount of work done when the point of application of a one-newton force moves one meter in the direction of the force.

The joule unit of measurement is named after British scientist James Prescott Joule.

Joule is represented by the letter ‘J.’

Kilojoule and megajoule are higher units of work.

11kilojoule=1000J=1000J

11 kilojoule=103J=103J or,

11megajoule=1000,000J=1000,000J

11megajoule=106J=106J

**Energy:**

Anything that can work has energy. The capacity to work is defined as energy. The amount of work that a body can accomplish is how much energy it has. As a result, the SI unit of energy is the joule.

**Different Forms of Energy:**

Mechanical energy, thermal energy, electrical energy, and chemical energy are examples of diverse types of energy. We’ll look at mechanical energy in this chapter. Mechanical energy is divided into two types: kinetic energy and potential energy.

**Kinetic Energy:**

A fast-moving stone can break a windowpane, falling water can crank turbines, and moving air can rotate windmills and drive sailboats, as we all know. The moving body in all of these situations has energy. The body in motion does the work. Kinetic energy is the form of energy that is possessed by moving objects.

“Kinetic energy is defined as the energy that an object possesses as a result of its motion. The letter ‘T’ is used to symbolize kinetic energy. Kinetic energy is present in all moving objects.”

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