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.

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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:

1. A force must act on an object. 💪
2. 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:

1. Mechanical energy (potential energy + kinetic energy)
2. Heat energy
3. Chemical energy
4. Electrical energy
5. 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:

1. Gravitational potential energy (due to an object’s height)
2. 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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