Chapter 7 · NCERT Class 9 Science

Motion

How far, how fast, which way, and is it speeding up? Six precise words separate "I moved a lot" from physics. Tap each to see exactly what it means.

🏃 3 topics⏱ ~25 min📝 12-question quiz

Play with it

The six words of motion

Everyday speech blurs them; physics keeps them sharp. Tap each term to see what it measures, its unit, and how it differs from its neighbour.

Explore · Describing motiontap a term

Learn

The three big ideas

Distance — total path length covered. A scalar (magnitude only).
Displacement — straight-line change in position, with direction. A vector.
Go out and come back → distance is large, but displacement is zero.

Speed = distance ÷ time (m/s). Velocity = displacement ÷ time, with direction.
Acceleration = change in velocity ÷ time (m/s²).

Worked example. A car speeds up from 0 to 20 m/s in 4 s. Find its acceleration.

a = (final − initial velocity) ÷ time = (20 − 0) ÷ 4 = 5 m/s².

Common mistake: treating speed and velocity as the same. Average speed uses total distance; average velocity uses displacement — they differ whenever the path isn't a straight line to the destination.

Distance–time graph: the slope = speed. A straight line means uniform (constant) speed.
Velocity–time graph: the slope = acceleration, and the area under it = distance travelled.

Where you'll meet it

Motion, measured

Speedometers & fitness apps

A speedometer shows instantaneous speed; a running app uses GPS positions over time to compute your speed, pace and distance — exactly these formulas.

Road safety

Braking distance grows with speed and depends on deceleration (negative acceleration) — the physics behind speed limits and stopping distances.

Check yourself

Competency quiz

Modelled on the competency-based pattern — MCQ, assertion–reason and a case study, testing whether you can use the ideas, not just recall them.

Score 0/12

Buffyyour study buddy

Hi! Ask me about distance vs displacement, speed, velocity, acceleration or motion graphs.

Buffy is an AI helper and can be wrong — always check your NCERT textbook.