Motion Complete Class 9 Science Revision Notes 2026-27

Motion Class 9 Science Notes: Motion is one of the most important topics in CBSE Class 9 Science because it helps students understand how objects move around us in daily life. Whether it is a moving car, a running athlete, a flying bird, or even the Earth revolving around the Sun, all these examples are related to motion. These Motion Class 9 Science Notes are designed to explain the chapter in simple words so that students can easily understand the basic concepts and prepare well for exams.

In these motion class 9 science Chapter 8 notes, students will learn about distance, displacement, speed, velocity, acceleration, and graphical representation of motion. The chapter also explains uniform and non-uniform motion with easy examples from real life. Understanding these concepts is very important because they form the base for higher classes and future physics topics.

These Class 9 Notes are prepared according to the latest NCERT and CBSE Board syllabus and can be useful for quick revision before tests and annual examinations. Students looking for motion class 9 science notes PDF Download can use these notes to revise key concepts in a short time. Along with theory, these notes also support motion chapter class 9 science ncert solutions notes and help students improve their problem-solving skills. If studied carefully, this chapter becomes quite easy and intresting to learn.

Physics, Mechanics, and Their Branches

• Physics (Greek: Nature) is the branch of science that studies natural laws and their manifestation in natural phenomena.
• Mechanics — the oldest branch of physics — deals with rest and motion of material objects. It has three sub-branches:

Rest and Motion

• Rest: An object is at rest if its position does not change with respect to its surroundings with the passage of time.
• Motion: An object is in motion if its position changes continuously with respect to its surroundings (or observer) with time.

Rest and Motion are Relative

Motion depends on the observer's position. A passenger sitting in a moving car is at rest relative to other passengers but in motion relative to a person standing on the road. There is no such thing as absolute motion — even our classroom is "moving" as the Earth rotates and revolves.

Point Object

When the size of an object is much smaller than the distance it travels, it can be treated as a point object (e.g., Earth is a point object when studying its motion around the Sun).

Frame of Reference

To locate an object, we choose three mutually perpendicular axes (x, y, z). If any coordinate changes with time, the object is in motion w.r.t. that frame.

Types of Motion

Based on Dimensions

Based on Nature

• Linear (translatory) motion — moving car, falling stone.
• Rotational motion — electric fan, Earth about its axis.
• Oscillatory motion — simple pendulum, mass on a spring (to-and-fro motion).

Scalar and Vector Quantities

A vector is represented by a directed line segment drawn to scale — the length shows magnitude, the arrowhead shows direction.

Distance and Displacement

• Distance: The actual length of the path travelled by a body. Scalar, always positive, never decreases.
• Displacement: The shortest distance from initial to final position, in a specific direction. Vector, can be positive, negative, or zero.

Key Differences

If a body returns to its starting point, displacement = 0, but distance ≠ 0.

SI unit of both: metre (m).

Uniform and Non-Uniform Motion

• Uniform motion: Equal distances covered in equal intervals of time. Distance–time graph is a straight line.
• Non-uniform motion: Unequal distances in equal intervals of time. Distance–time graph is a curved line. Non-uniform motion is also called accelerated motion.

Example of non-uniform motion: a freely falling ball covers 4.9 m in the 1st second, 14.7 m in the 2nd second, 24.5 m in the 3rd second, and so on.

Speed

Speed = Distance ÷ Time ; s = d/t

• Scalar quantity. SI unit: m/s (also km/h; 1 km/h = 5/18 m/s).

Types

• Uniform speed — equal distances in equal time intervals.
• Variable (non-uniform) speed — unequal distances in equal time.
• Average speed = Total distance ÷ Total time
• Instantaneous speed — speed at a particular instant (shown on a vehicle's speedometer).

Velocity

Velocity = Displacement ÷ Time = distance travelled per unit time in a given direction.

• Vector quantity. SI unit: m/s.
• Magnitude of velocity = speed.

Speed vs Velocity

Types of Velocity

• Uniform velocity — equal distances in equal times in the same direction.
• Non-uniform velocity — unequal distances in equal times, or change in direction (even at constant speed). A car moving on a circular road at constant speed has non-uniform velocity.
• Average velocity (for uniform acceleration): v_av = (u + v)/2
• Average velocity (general): Total displacement ÷ Total time
• Instantaneous velocity — velocity at a particular instant.

When is average speed equal to magnitude of average velocity? When the body moves along a straight line in the same direction (so distance = magnitude of displacement).

Acceleration

Acceleration = Change in velocity ÷ Time taken ; a = (v − u)/t

• Vector quantity. SI unit: m/s². CGS: cm/s².

Types

• Uniform acceleration — velocity changes by equal amounts in equal time (e.g., freely falling body).
• Non-uniform acceleration — unequal change in equal time (e.g., car in traffic).
• Positive acceleration — velocity increases in the direction of motion.
• Negative acceleration (retardation/deceleration) — velocity decreases (e.g., a train slowing down).

Three Equations of Uniformly Accelerated Motion

For an object with initial velocity u, final velocity v, uniform acceleration a, time t, and displacement s:

• v = u + at (1st Equation - velocity - time)
• s = ut + 1/2 at² (2nd Equation - Position - time)
• v² = u² + 2as (3rd Equation - velocity - poistion)

Distance Covered in the nth Second

S_n^th = u + a/2 (2n - 1)

Tips for Solving Numericals

1. Body dropped from height → u = 0.
2. Body comes to rest / reaches highest point → v = 0.
3. Uniform velocity → a = 0.
4. Free fall → only force acting is gravity.

Motion Under Gravity

Acceleration due to gravity: g = 9.8 m/s² (use 10 m/s² only if specified).

• A body projected vertically up returns to the point of projection with the same speed in the opposite direction.
• Time of ascent = Time of descent.

Class 9 Science Motion Chapter Solved Examples

Q. A car moves at 50 km/h. Two seconds later, its speed is 60 km/h. Find the acceleration.

Solution: u = 50 km/h = 250/18 m/s ; v = 60 km/h = 300/18 m/s ; t = 2 s

a = v-u/t = 300/18 -250/18/2 = 50/18/2 ≈ 1.39 m/s²

Q. A car attains 54 km/h in 20 s after it starts. Find the acceleration.

Solution: u = 0, v = 54 km/h = 15 m/s, t = 20 s

a = 15 − 0/20 = 0.75 m/s² 

Q. A ball is thrown vertically upward at 20 m/s. How high does it rise? (g = 9.8 m/s²)

Solution: u = 20, v = 0, a = −9.8 m/s²

0 − 400 = 2 × (−9.8) × s ⇒ s = 400/19.6 ≈ 20.4 m 

Q. A car covers the first half of a journey at 40 km/h and the second half at 60 km/h. Find the average speed.

Solution: For two halves at speeds v₁ and v₂:

V_av = 2v₁v₂/v₁ + v₂ = 2 × 40 × 60/40 + 60 = 48 km/h

Q. A bus goes one way at 54 km/h and returns at 36 km/h. Average speed for the whole journey?

Solution: V_av = 2 × 54 × 36/54 + 36 = 3888/90 = 43.2 km/h

Distance from Velocity–Time Graph

Distance covered = Area under the v–t graph.

• Uniform speed: v–t graph is a horizontal line; distance = rectangle area = v × t.
• Uniform acceleration: v–t graph is a slanting straight line; distance = area of trapezium.
• Variable acceleration: v–t graph is a curve; distance = sum of areas of thin strips.

Graphical Derivation of the Three Equations

From a velocity–time graph showing initial velocity u (at point P) and final velocity v (at point Q) over time t:

1. First equation: Slope of PQ = acceleration → a = (v − u)/t → v = u + at.
2. Second equation: Area under v–t graph = OP × t + ½ × (v − u) × t = ut + ½at² → s = ut + ½at².
3. Third equation: Area of trapezium = ½(u + v) × t and substituting t = (v − u)/a gives v² = u² + 2as.

Circular Motion

Circular motion is the motion of a body along a circular path. Uniform circular motion means constant speed — but the direction of velocity changes continuously, so the motion is accelerated.

Why Accelerated?

In uniform circular motion, speed is constant but velocity changes (because direction changes). Since acceleration is the rate of change of velocity, the motion is accelerated.

Uniform Linear vs Uniform Circular Motion

Examples of uniform circular motion: Moon around Earth, satellites around planets.

Radian, Angular Displacement and Angular Velocity

Radian

One radian is the angle subtended at the centre of a circle by an arc whose length equals the radius.

θ = ℓ/r radian

Full circle: 2π radians = 360°

• 1 radian ≈ 57.3°

Angular Displacement (θ)

The angle (in radians) swept by a body at the centre of the circle in a given time. SI unit: radian.

Angular Velocity (ω)

Angular displacement per unit time:

ω = θ/t or ω=2π/T = 2πN

where T = time period, N = frequency. SI unit: rad/s.

Relation Between Linear and Angular Quantities

v = rω

where v = linear velocity, r = radius, ω = angular velocity.

Class 9 Science Motion Chapter 7 Formulas