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ATP EducationScience Exploration Notes Class 9 English Medium 2026-27
Science Exploration Notes Class 9 English Medium 2026-27 now available for students studying in cbse school, up board, state boards and international cbse schools and Latest CBSE Curriculum based on NCERT books.
Science Exploration Notes Class 9 English Medium 2026-27
All topics of Chapter 7
1. Chapter Review and Key Points 2. Work in Science 3. Work And Energy 4. Potential Energy 5. Simple Machine And Power 6. Conservation of Mechanical Energy 7. Assignments - What Have You Learned?Science Exploration Chapter 7. Work, Energy, and Simple Machines
CBSE Notes New Syllabus: Class 9
Assignments - What Have You Learned?
Chapter 7. Work, Energy, and Simple Machines
This section explains potential energy, mechanical energy, and the law of conservation of mechanical energy. It also describes how energy continuously changes from one form to another in nature and in everyday life. These concepts help us understand the working of pendulums, roller coasters, hydroelectric power stations and many other real-life systems.
Potential Energy
Potential energy is the energy possessed by an object because of its position or configuration. An object placed at a height stores energy due to the force of gravity.
Definition
Potential energy is the energy possessed by an object due to its position or shape.
Types of Potential Energy
- Gravitational Potential Energy – Energy stored because of the object's height above the ground.
- Elastic Potential Energy – Energy stored in stretched or compressed elastic objects such as springs and rubber bands.
Gravitational Potential Energy
When an object is lifted above the ground, work is done against gravity. This work is stored in the object as gravitational potential energy.
Formula
Potential Energy (PE) = m × g × h
Where
- m – Mass of the object (kg)
- g – Acceleration due to gravity (9.8 m/s²)
- h – Height above the ground (m)
SI Unit
The SI unit of potential energy is Joule (J).
Factors Affecting Potential Energy
- Mass – Greater the mass, greater the potential energy.
- Height – Greater the height, greater the potential energy.
- Gravity – Potential energy depends on the value of gravitational acceleration.
Examples of Potential Energy
- Water Stored in a Dam – Water at a height possesses gravitational potential energy.
- Book on a Shelf – The raised book stores potential energy.
- Stretched Rubber Band – Stores elastic potential energy.
- Drawn Bow – Energy is stored before releasing the arrow.
Mechanical Energy
Mechanical energy is the total energy possessed by an object because of its motion and position.
Definition
Mechanical energy is the sum of kinetic energy and potential energy.
Formula
Mechanical Energy = Kinetic Energy + Potential Energy
ME = KE + PE
Law of Conservation of Mechanical Energy
The total mechanical energy of an isolated system remains constant if no external force such as friction causes energy loss. Energy continuously changes between kinetic energy and potential energy, but the total remains the same.
Statement
Mechanical energy can neither be created nor destroyed. It only transforms from one form into another while the total mechanical energy remains constant.
Energy Transformation
| Situation | Energy Conversion |
|---|---|
| Object Falling from a Height | Potential Energy → Kinetic Energy |
| Object Lifted Upward | Kinetic Energy → Potential Energy |
| Hydroelectric Power Plant | Potential → Kinetic → Electrical Energy |
| Bow and Arrow | Elastic Potential → Kinetic Energy |
| Roller Coaster | Potential ↔ Kinetic Energy |
Applications of Mechanical Energy
- Hydroelectric Dams – Stored water produces electricity.
- Pendulums – Energy changes continuously between potential and kinetic forms.
- Roller Coasters – Height and speed keep changing while total mechanical energy remains nearly constant.
- Sports – Jumping, throwing and running involve continuous energy transformation.
- Windmills – Convert kinetic energy of moving air into electrical energy.
Difference Between Kinetic Energy and Potential Energy
| Kinetic Energy | Potential Energy |
|---|---|
| Energy due to motion. | Energy due to position. |
| Depends on mass and velocity. | Depends on mass and height. |
| Formula: K = ½mv² | Formula: PE = mgh |
| Zero when the object is at rest. | Can exist even when the object is at rest. |
ATP Education Concept Builder
Whenever an object moves upward, its kinetic energy gradually changes into potential energy. As it moves downward, the stored potential energy changes back into kinetic energy. This continuous conversion explains the conservation of mechanical energy.
ATP Education Exam Booster
- Remember the formula PE = mgh.
- Learn the difference between kinetic and potential energy.
- Understand the law of conservation of mechanical energy with real-life examples.
- Practise questions based on energy transformation.
- Hydroelectric plants, roller coasters and pendulums are important CBSE examples.