Chapter 2 of 25

Tamil Nadu (TNBSE)Class 9 Science★ 4-6 marks in assessments

Motion

Samacheer Kalvi (TN State Board) Class 9 Science — Physics Chapter 2, Motion. Motion describes how objects change position over time. Understanding speed, velocity, acceleration, and equations of motion is essential for engineering, space exploration, and everyday transport. Notes, worked examples, common mistakes, and quick revision.

⏱ 20 min readMedium difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Distinguish distance from displacement, and speed from velocity
2Calculate uniform and non-uniform acceleration
3Derive and apply the equations of motion
4Explain uniform circular motion

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Why this chapter matters

Motion describes how objects change position over time. Understanding speed, velocity, acceleration, and equations of motion is essential for engineering, space exploration, and everyday transport.

Before you start — revise these

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Class 8 Science — Force and Pressure

Basics of force and motion.

Motion — Class 9 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 9 Science, Physics — Chapter 2. Motion describes how objects change position over time. Understanding speed, velocity, acceleration, and equations of motion is essential for engineering, space exploration, and everyday transport.

1. About this chapter

This chapter explores motion, classifying it into uniform and non-uniform types, deriving equations of motion graphically, and analyzing circular paths.

2. Velocity and Acceleration

Velocity: Rate of change of displacement ( $v = s / t$ , measured in m/s).
Acceleration: Rate of change of velocity ( $a = (v - u) / t$ , measured in m/s²).

3. Equations of Motion

For uniform acceleration, the three equations of motion are:

$v = u + a t$
$s = ut + rac{1}{2}at^2$
$v^{2} = u^{2} + 2 a s$

4. Circular Motion

When an object moves in a circular path with constant speed, it is called uniform circular motion. The acceleration is directed towards the center (centripetal acceleration).

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

First Equation of Motion

v = u + a t

u = initial velocity, v = final velocity, a = acceleration, t = time.

Second Equation of Motion

s = u t + 0.5 a t²

s = displacement.

Third Equation of Motion

v² = u² + 2 a s

Relates velocities and displacement.

Uniform Circular Velocity

v = 2 pi r / t

r = radius of the circular path.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Treating distance and displacement as identical.

✓ Distance is the actual path length (scalar); displacement is the straight-line shortest path (vector with direction).

WATCH OUT

✗ Forgetting to convert units to SI.

✓ Always convert km/h to m/s by multiplying by 5/18 before calculations.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Multiple Choice Questions

Questions on distance-time graphs and circular motion.

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Numerical Problems

Calculations based on equations of motion.

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Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1MEDIUM· Numerical

A car accelerates from rest at 2 m s⁻² for 10 s. Find the distance traveled.

▶ Show solution

u = 0, a = 2, t = 10. s = ut + 0.5at² = 0 + 0.5 * 2 * (100) = 100 m.

Q2EASY· Concept

What is uniform circular motion? Give two examples.

▶ Show solution

Motion of an object along a circular path with constant speed is uniform circular motion. Examples: 1. Revolution of the Earth around the Sun. 2. Motion of the tip of a watch hand.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Distance is scalar; displacement is vector.
•Acceleration a = (v - u) / t.
•Equations of motion: v = u+at, s = ut+0.5at², v² = u²+2as.
•In circular motion, velocity direction changes continuously.

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 4-6 marks in assessments

Question type	Marks each	Typical count	What it tests
MCQ	1	1-2	Base concepts and definitions
Short Answer	2-3	1-2	Descriptive and application points

Prep strategy

Understand core definitions and solve standard textbook problems.
Review common mistakes to avoid losing easy marks.

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Automotive Safety

Equations of motion help engineers calculate safe braking distances for vehicles under different speeds.

Satellite Orbits

Uniform circular motion principles determine the speed required for satellites to remain in stable orbits.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Write definitions precisely as defined in the textbook.
Draw neat, labeled diagrams for biology and physics chapters.

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Read advanced reference materials to explore concepts beyond the school syllabus.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

Class 9 Annual ExamsHigh

NTSE Stage 1Medium

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

Yes. If an object returns to its starting point, the shortest distance (displacement) is zero, but the actual path covered (distance) is non-zero.

Though the speed is constant, the direction of motion changes continuously at every point, indicating a change in velocity (acceleration).

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