Download Describing Motion Around Us – NCERT Class 9 Science Chapter 4 PDF from the new NCERT Class 9 Science book Exploration (2026-27). Read the chapter online or download the free PDF. Position is the distance and direction of an object from a chosen reference point at a given instant. An object is in motion if its position changes with time; at rest if it does not.
Describing Motion Around Us PDF – Chapter 4 of Exploration
Read the chapter online or download the PDF.
| Chapter | Download | |
|---|---|---|
| Chapter 4 PDF | Describing Motion Around Us | View PDF |
| Full book | NCERT Class 9 Science – Exploration | View Book |
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What Is in Describing Motion Around Us? (Class 9 Science Chapter 4)
- Position is the distance and direction of an object from a chosen reference point at a given instant. An object is in motion if its position changes with time; at rest if it does not.
- Total distance travelled counts the whole path; displacement is only the net change in position, and it needs a direction as well as a magnitude. Magnitude of displacement ≤ total distance travelled, always.
- Average speed = total distance travelled / time interval. Average velocity = displacement / time interval. Both have the SI unit m s⁻¹, but only velocity carries a direction.
- Average acceleration = change in velocity / time interval, SI unit m s⁻². It points along the velocity when the speed is rising and opposite to it when the speed is falling.
- On a position–time graph the slope is velocity: a straight line means constant velocity, a curve means accelerated motion. On a velocity–time graph the slope is acceleration and the area under the line is the displacement.
- For constant acceleration: v = u + at, s = ut + ½at², v² = u² + 2as. These three follow from the definitions, not from memory.
- In uniform circular motion the speed is constant but the direction of velocity (along the tangent) changes every instant — so the motion is accelerated. In one revolution the distance is 2πR and the displacement is zero.
Quick revision – Describing Motion Around Us
| Quantity | What it means | SI unit | Key point |
|---|---|---|---|
| Position | Distance and direction from the reference point at an instant | M | Needs a fixed reference point and a sign convention |
| Distance travelled | Total length of the path actually covered | M | Never decreases; no direction |
| Displacement (s) | Net change in position between two instants | M | Has direction; magnitude ≤ distance travelled |
| Average speed | Total distance travelled ÷ time interval | M s⁻¹ | No direction; zero only if the object never moves |
| Average velocity (vav) | Displacement ÷ time interval | M s⁻¹ | Can be zero even when the average speed is not |
| Average acceleration (a) | Change in velocity ÷ time interval | M s⁻² | Negative sign = acceleration opposite to the velocity |
| Slope of position–time graph | Rate of change of position | M s⁻¹ | Gives the velocity |
| Slope of velocity–time graph | Rate of change of velocity | M s⁻² | Gives the acceleration |
| Area under velocity–time graph | Velocity × time interval | M | Gives the displacement |
| Kinematic equations | V = u + at, s = ut + ½at², v² = u² + 2as | — | Valid only when the acceleration is constant |
| Uniform circular motion | Circular path at constant speed | — | Accelerated, because the direction of velocity keeps changing |
| Speed in one revolution | Vav = 2πR/T | M s⁻¹ | Average velocity over one full revolution is zero |
Old NCERT vs New – Class 9 Science
In the old NCERT Class 9 Science book, Chapter 4 was “Structure of the Atom” and motion was Chapter 7. In the new Exploration book, motion is Chapter 4, and the atom is now in Chapter 8, “Journey Inside the Atom”.
Solutions and All Chapters
Answers to the exercises and the full chapter list of Exploration:
Describing Motion Around Us – Overview
| Class | Class 9 |
| Subject | Science |
| Book | Exploration – new NCERT book |
| Chapter | 4 of 13 – Describing Motion Around Us |
| Book pages | 48 – 71 |
| Edition | Latest NCERT edition (2026-27) |
| Session | 2026-27 |
| Free – read online or download |
Class 9 Science Chapter 4 – FAQs
Where can I download Describing Motion Around Us Class 9 PDF?
From the download table on this page – the chapter PDF is free, and the full book is linked too.
What is Class 9 Science Chapter 4 about?
Position is the distance and direction of an object from a chosen reference point at a given instant. An object is in motion if its position changes with time; at rest if it does not.
Is Describing Motion Around Us from the new NCERT Class 9 Science book?
Yes. It is chapter 4 of exploration, the new NCERT Class 9 Science book for 2026-27.
Is this the latest NCERT edition for 2026-27?
Yes – the PDF is NCERT’s latest edition for the 2026-27 session.
Where are the NCERT Solutions for Class 9 Science Chapter 4?
Open the NCERT Solutions link above for answers to the exercise questions.