CBSE Notes Class 9 Science Chapter 8 - Force and Laws of Motion

A force is a push or pull exerted on an object due to its interaction with another object. As a vector quantity, force has both magnitude and direction. Forces can cause objects to accelerate, decelerate, alter their direction, or change their shape. Sir Isaac Newton developed three fundamental laws of motion that define the relationship between a body, the forces acting on it, and its resulting motion.

1.0Download CBSE Class 9 Science Chapter 8 Force and Laws of Motion: Free PDF

Get ready to strengthen your Science fundamentals with our free PDF notes for CBSE Class 9 Science Chapter 8 Force and Laws of Motion. These notes are carefully crafted to help students grasp key concepts such as inertia, momentum, Newton’s laws of motion, and the mathematical derivations with ease.

Class 9 Science Chapter 8 Revision Notes:

2.0Force and Motion

Force is an external influence that alters a body's state of rest or its uniform straight-line motion.
Motion-Motion refers to the change in an object's position relative to a chosen reference point or frame of reference. It is a core concept that describes how objects move through space over time.

Also Read: Motion and its type

3.0Effects of Force

It can transform the shape and size of an object.
It can move a stationary object.
It can bring a moving object to a stop.
It can either speed up or slow down a moving object.
It can transform the direction of a moving object..

4.0Balanced and Unbalanced Forces

Resultant Force-The resultant force is the single force that, when applied to a body, produces the same effect as the combined effect of multiple forces acting on that body.

Balanced Forces- If the vector sum of all the forces acting on a body is zero.

In such cases the acceleration of the object is zero,and its velocity remains constant.
If the total force acting on the object is zero,the object either remains at rest or continues to move with constant velocity.
FNet=0

Unbalanced Forces-If the net force exerted on an object is not zero,then the force acting on it is said to be unbalanced.

Acceleration of the object is not zero and its velocity changes.
If the total force acting on an object is not zero then such a force changes state of rest or the state of uniform motion.
FNet≠0

5.0Inertia and Mass

Inertia-The property of matter that causes it to resist changes to its state of rest or uniform straight-line motion is known as inertia. Inertia can be categorized into three types:

Inertia of Rest
Inertia of Motion
Inertia of Direction

Mass-Mass is a measure of the quantity of matter in an object or substance. It is a key property that indicates how much an object resists changes in its motion and how it interacts with gravitational forces. Mass is calculated in grams (g) or kilograms (kg).

Mass is a quantitative measure of Inertia ,more the mass ,more will be the inertia and vice-versa.

6.0Newton’s First Laws of Motion

An object will remain at pause or continue to move in a straight line path at a constant speed unless external force act upon him.
Every object has a natural tendency to resist changes to its state of rest or motion, and this resistance is known as inertia.

7.0Key Features of CBSE Class 9 Science Notes Chapter 8 Force and Laws of Motion

Aligned with the latest CBSE syllabus, these notes present the concepts in a clear and concise manner, making learning more effective and revision quicker.
Each topic is explained using easy language, real-life examples, and illustrations to help students relate the concepts to everyday experiences.
Whether you're revising for exams or trying to build strong fundamentals, these notes serve as a reliable companion for mastering Chapter 8.
With detailed explanations and key highlights, these CBSE notes make it easier to understand the logic behind the laws and apply them in numerical problems.
The downloadable PDF format ensures you can study from any device, even without internet access, giving you the freedom to learn anytime, anywhere.