Chapter – 10
Work and Energy
In this post we have given the detailed notes of class 9 Science Chapter 10 (Work and Energy) in English. These notes are useful for the students who are going to appear in class 9 board exams.
| Board | CBSE Board, UP Board, JAC Board, Bihar Board, HBSE Board, UBSE Board, PSEB Board, RBSE Board |
| Textbook | NCERT |
| Class | Class 9 |
| Subject | Science |
| Chapter no. | Chapter 10 |
| Chapter Name | (Work and Energy) |
| Category | Class 9 Science Notes in English |
| Medium | English |
Class 9 Science Chapter 10 (Work and Energy) in English
Chapter 10: Work and Energy
What is work? 🤔
In science, work is done only when a force causes an object to move.
Conditions for work to be done:
- A force must act on an object. 💪
- The object must move a distance in the direction of the force. ➡️
- Example:
Pushing a box across the floor: Work is done because you apply a force and the box moves.
10.1.3 Work Done by a Constant Force
- Formula:
Work (W) = Force (F) x Distance (s)
- Unit:
Joule (J)
1 J = 1 Nm (newton meter)
- Example:
If you push a box with a force of 10 N and it moves 5 m, the work done is 50 J.
10.2 Energy ⚡
- What is energy?
Energy is the ability to do work.
- Forms of energy:
- Mechanical energy (potential energy + kinetic energy)
- Heat energy
- Chemical energy
- Electrical energy
- Light energy
10.2.2 Kinetic Energy 🏃
- What is kinetic energy?
Kinetic energy is the energy an object has due to its motion.
- Formula:
Kinetic Energy (Ek) = 1/2 x Mass (m) x Velocity (v)^2
- Example:
A moving car has kinetic energy.
10.2.3 Potential Energy 📚
- What is potential energy?
Potential energy is the stored energy an object has due to its position or configuration.
- Types of potential energy:
- Gravitational potential energy (due to an object’s height)
- Elastic potential energy (like in a stretched rubber band)
- Formula for gravitational potential energy:
Potential Energy (Ep) = Mass (m) x Acceleration due to gravity (g) x Height (h)
- Example:
A book on a shelf has gravitational potential energy.
10.2.6 Law of Conservation of Energy 🔄
- What is the law of conservation of energy?
Energy cannot be created or destroyed, only transformed from one form to another.
- Example:
When a ball falls, its potential energy is converted into kinetic energy.
10.3 Rate of Doing Work ⏱️
- What is power?
Power is the rate at which work is done.
- Formula:
Power (P) = Work (W) / Time (t)
- Unit:
Watt (W)
1 W = 1 J/s (joule per second)
- Example:
A light bulb with a higher wattage uses more energy per second.
Key Points to Remember
- Work and energy are closely related concepts.
- Energy exists in many different forms and can be converted from one form to another.
- The total energy of a system remains constant, even during energy transformations.
- Power is a measure of how quickly work is done.
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