Understanding Work and Energy is essential for scoring well in CBSE Class 9 Science. This chapter explains how force causes motion, how energy is transferred, and how work and energy are closely connected in everyday life.
These Class 9th Work and Energy Notes are written in simple language, strictly based on the CBSE Class 9 Science syllabus, and focus on concepts, formulas, and exam-oriented points.
Work and Energy Class 9 Notes are given here in PDF format. These notes help students understand and remember key ideas effectively.
What is Work and Energy?
Work and energy are basic concepts in physics. Work is done when a force causes an object to move.
Energy is the ability to do this work. Understanding Work And Energy Class 9 Notes will help students explain many everyday events, from simple movements to how machines function.
This chapter lays the groundwork for further studies in mechanics and energy transformations.
Class 9th Work And Energy Notes
The chapter Work and Energy Class 9 introduces the scientific meaning of work, which is different from its everyday usage. In physics, work is said to be done only when a force applied on an object causes displacement in the direction of the force.
Conditions for Work
For work to occur in physics:
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A force must act on an object.
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The object must move (be displaced).
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The displacement should not be perpendicular to the force.
If a person pushes a wall that does not move, no work is done, even if the person feels tired.
Formula for Work
Work (W) is the product of force (F) and displacement (S) in the direction of the force.
Work is a scalar quantity, meaning it has magnitude but no direction.
The SI unit of work is Joule (J). One Joule is the work done when a force of 1 Newton moves an object by 1 meter. Another unit of work is erg.
What is Energy?
Energy is the ability to do work. Its SI unit is also Joule (J). One Joule of energy is the amount needed to do 1 Joule of work. Energy exists in many forms, including heat, light, chemical, electrical, mechanical, and sound energy.
Kinetic Energy
Kinetic energy is the energy possessed by an object because it is moving. The faster an object moves or the more mass it has, the more kinetic energy it carries. Kinetic energy depends on:
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The object's mass (m).
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The object's speed (v).
Potential Energy
Potential energy (PE) is the energy an object has due to its position or arrangement. For example, a stretched rubber band or an object raised to a height stores potential energy.
Potential energy due to height:
where m is mass, g is acceleration due to gravity, and h is height.
Difference Between Work And Energy
In Class 9 Science, work and energy are closely related but not the same. Work is said to be done only when a force applied to an object causes displacement in the direction of the force.
On the other hand, energy is the ability or capacity of an object to do work. An object may have energy even when no work is being done at that moment.
Work is an action, while energy is a property of an object. Work is measured as the product of force and displacement, whereas energy exists in different forms such as kinetic energy and potential energy. When work is done on an object, its energy changes, showing that work is a way of transferring energy from one object to another.
What is the Law of Conservation of Energy?
This law states that energy can neither be created nor destroyed. It only changes from one form to another.
The total energy in a closed system stays constant. For example, an electric fan changes electrical energy into kinetic energy.
What is Power?
Power is the rate at which that energy is being used. It tells you how "hungry" an appliance is for electricity at any given moment.
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Definition: The amount of electrical energy transferred or consumed per unit of time.
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Unit: Measured in Watts (W) or Joules per second (J/s).
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Formula: P = V * I
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Where V is Voltage (Potential Difference) and I is Current.
Electrical energy is the total amount of work done by an electric current over a period of time. Think of it as the "total fuel" consumed by an appliance.
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Definition: The capacity to do work by moving electric charges through a conductor.
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Unit: The SI unit is the Joule (J). However, for household bills, we use Kilowatt-hours (kWh).
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Formula: E = P * t
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Where P is Power and t is Time.
Work And Energy Class 9 PDF
Class 9th Work and Energy Notes PDF is given here to help students revise the chapter quickly and understand concepts without confusion. The notes explain important topics such as work, energy, power, kinetic energy, potential energy, and the law of conservation of energy in a structured manner.
This Work and Energy Class 9 PDF is especially useful for last-minute revision, practice, and self-study. Students can download and access the notes from here.