CBSE Class 9 Science Notes Chapter 10 Work and Energy

Work and energy are fundamental concepts that explain how and why things move. In simple terms, work is done when a force causes an object to move, and energy is the ability to do that work. From lifting a school bag to riding a bicycle or switching on a fan, the principles of work and energy are involved in many everyday activities.

These CBSE Class 9 Science Notes Chapter 10 – Work and Energy provide a clear and exam-oriented explanation of the entire chapter as per the latest CBSE syllabus. In this chapter, you will learn about work done by a force, kinetic energy, potential energy, mechanical energy, the law of conservation of energy, and power. Our well-structured work and energy class 9 notes highlight key formulas, important definitions, numerical problem-solving methods, and conceptual explanations in a simple format.

1.0Download CBSE Notes Class 9 Science Chapter 10 Work and Energy: Free PDF

Students can now download the CBSE Class 9 Science Chapter 10 Work and Energy notes for free in a well-organized PDF format. These notes are designed to help students grasp fundamental concepts in Physics, such as work, energy, power, and the different forms of energy, including kinetic and potential energy.

2.0Concept of Work

• Work is done on an object when a force causes a displacement of the object.

Conditions that must satisfied for work to be done:

1. A force should act on an object.
2. The object must be displaced.
3. The direction of Force must not be perpendicular to the displacement

Mathematical Definition of Work

1. A constant force is applied in the direction of the displacement of an object.

Work = Force ✕ displacement

W = F ✕ s

2. A Constant force is applied at a certain angle with the direction of the displacement of an object.

W = Fs Cos $\theta$

• Work is a scalar quantity.
• SI Unit of work is Joule.
• CGS Unit is Erg

Some important Points related to work

1. If $\theta$ = 0° then Cos 0° = 1 and W = F ✕ s
2. If $\theta$ = 90° then W = 0
3. If $\theta$ = 180° then Cos 180° = -1 then W = -F ✕ s

Concepts of Positive and Negative Work

• When angle between the force and displacement is acute i.e. 0°< $\theta$ < 90° The work done is positive.
• When angle between the force and displacement is obtuse i.e. 90°< $\theta$ < 180° The work done is negative.
• Whenever force is in the direction of motion, velocity of the object increases and work done is positive.
• Whenever force opposes motion, velocity of object decreases and the work done is negative.
• Work is positive when force and displacement are parallel to each other and that are in the same direction and work is negative when force and displacement are antiparallel to each other.

Condition for Zero Work

Also Read: Work-Energy Theorem

3.0Energy

• Energy is the capacity to do work, its unit is the same as that of work that is Joule(J).
• IJ is the energy required to do 1 Joule of work. Sometimes a larger unit of energy called KiloJoule(kJ) is used. IKJ = 1000J

4.0Forms of Energy

The world around us offers energy in various forms, including potential energy, kinetic energy, thermal energy, chemical energy, electrical energy, and light energy.

1. Mechanical Energy-The capacity to do mechanical work is called mechanical energy. Mechanical energy is of two types:

(a) Kinetic energy       

(b) Potential energy

Mechanical Energy = Kinetic Energy + Potential Energy

Also Read: Work, Energy and Power

5.0Key Features of Class 9 Science Notes Chapter 10 Work and Energy

• Complete Coverage: Includes all key topics such as work, energy, power, types of energy, law of conservation of energy, and numerical problems related to work and energy.
• Clear and Concise Explanations: Concepts are explained in simple and easy-to-understand language, making it easier for students to grasp complex topics.
• Aligned with CBSE Curriculum: These notes are strictly in accordance with the latest CBSE syllabus and the NCERT textbook, ensuring all essential concepts are covered.
• Formulae and Definitions: Essential formulas, definitions, and units related to work, energy, and power are clearly highlighted for quick reference.