CBSE Class 9 Science Notes Chapter 8 Motion

Home

Author at PW

February 19, 2026

Class 9 chapter motion notes are study materials that help students understand the movement of objects in a straight line. These notes cover key physical quantities like distance, displacement, speed, velocity, and acceleration. By using these simplified explanations, learners can master the three equations of motion and graphical representations, making complex physics concepts much easier to understand.

Check Out: Class 9th Books

What Does Class 9 Chapter Motion Notes Cover?

Before learning about distance, displacement, speed, velocity, and acceleration, let’s first understand the basic concept of motion.

What is Motion?

Motion is a change in the position of an object over time. To know if something moved, we need a "starting point" called a reference point or origin. If your distance from a tree changes while you walk, you are in motion relative to that tree.

Many students struggle to describe motion because they forget it is relative. Imagine sitting in a moving train. To you, the passenger sitting next to you isn't moving. However, to a person standing outside on the platform, both you and your friend are moving very fast. This shows that an object can be at rest and in motion at the same time depending on the observer.

Physical Quantities to Know

Class 9 motion chapter notes will show that measurements are of two types:

Scalar Quantities: These only describe "how much" (magnitude). Examples: distance and speed.
Vector Quantities: These describe "how much" and "in which direction." Examples: displacement and velocity.

What is the Difference Between Distance and Displacement

When studying CBSE Class 9 motion notes, the first challenge is separating distance from displacement. Many students use them interchangeably, but in Science, they represent different ideas about your journey.

Total Path vs Shortest Path

Distance: This is the total length of the actual path you walked. It doesn't care about direction. If you walk 5m East and 5m West, your distance is 10m.
Displacement: This is the shortest straight-line distance between where you started and where you ended. In the example above, your displacement is 0m because you ended up back at the start.

To help you visualize these differences for your exams, we have compared them in the table below. It highlights why displacement can be zero even if you have walked a long way.

Feature	Distance	Displacement
Type of Quantity	Scalar	Vector
Measurement	Total path length	Shortest straight-line path
Direction	Not required	Essential for calculation
Possible Values	Always positive	Positive, negative, or zero

Speed and Velocity in Motion Notes

A huge part of class 9 science chapter 8 notes involves calculating how fast things move. While we use these words similarly in daily life, science treats them differently. Speed is just about how fast you go, but velocity includes your direction.

Types of Speed and Velocity

Uniform Speed: Covering equal distances in equal time intervals.
Average Speed: The total distance divided by the total time taken.
Velocity: The displacement of an object per unit of time.
Changing Velocity: This happens if speed changes, direction changes, or both change.

General Best Practice: Always convert units to m/s before solving numerical problems to avoid simple calculation errors.

Check Out: Class 9 Sample Papers

How to Calculate Speed and Velocity Changes

In class 9 Science motion notes, we look at how fast things move. Speed and velocity might seem the same, but adding a direction turns speed into velocity. This change is vital for accurate physics calculations and understanding motion in a straight line.

Speed: The Rate of Motion

Speed is the distance covered per unit of time. It tells us the "rate" at which an object covers distance.

Formula: v = s / t
Average Speed: Since we rarely move at the same speed, we use: Total Distance / Total Time.

Velocity: Speed with Direction

Velocity is the speed of an object in a specific direction. For example, "50 km/h" is speed, but "50 km/h towards the North" is velocity. A change in velocity happens if the object speeds up, slows down, or simply turns a corner.

Uniform and Non-Uniform Motion

Uniform Motion: When an object covers equal distances in equal time gaps. A car on a straight highway with a locked speed is a good example.
Non-Uniform Motion: When an object covers unequal distances in equal time. This is what you see in city traffic where you stop and start constantly.

What Is Acceleration and Motion Graphs?

Acceleration is one of the most exciting parts of class 9 chapter 8 Science notes. It happens whenever your velocity changes. Most people think acceleration only means "speeding up," but in science, it also includes slowing down or changing direction.

What is Acceleration?

It is the rate of change of velocity. If a car goes from 0 to 60 km/h in 5 seconds, it is accelerating.

Formula: a = (v - u) / t (where v is final velocity and u is initial velocity).
Retardation: This is "negative acceleration." It happens when you hit the brakes and the object slows down.

Reading Motion Graphs

Graphs help us tell a story about motion without using many words. There are two main types you need to know for your class 9 Science chapter 8 notes:

Distance-Time Graph: The slope shows the speed. A straight line means constant speed, while a flat horizontal line means the object has stopped.
Velocity-Time Graph: The slope shows the acceleration. The area under the line tells you the total displacement (distance moved in a direction).

Check Out: Class 9th Revision Books

Equations of Motion and Circular Paths

The final section of our class 9 chapter motion notes focuses on the math used to predict movement. These three equations are the "golden rules" for objects moving in a straight line with constant acceleration.

The Three Kinematic Equations

Students should memorise these formulas for solving numerical problems:

First Equation: v = u + at (Relates velocity and time).
Second Equation: s = ut + 1/2at^2 (Relates position and time).
Third Equation: v^2 = u^2 + 2as (Relates position and velocity).

Uniform Circular Motion

When an object moves in a circle at a constant speed, we call it uniform circular motion. Even if the speed is steady, the direction is always changing. Since the direction changes, the velocity changes. This makes circular motion an accelerated motion.

Real-world examples include: