CBSE Class 9 · Science
Describing Motion Around Us
Official NCERT chapter from Science (Grade 9, 2026 edition) (book code iesc1). ExamMaster notes are original teaching at CBSE Class 9 depth.
This lesson follows the official chapter “Describing Motion Around Us” in Science (Grade 9, 2026 edition). The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.
- CBSE Class 9
- Medium level
- 8 concepts
1Motion in a Straight Line
Straight-line motion is a change of position along one agreed line. Distance is the walk-length; displacement is the signed change from start to now. A 3 m walk forward and 3 m back is 6 m of distance and 0 displacement.
Calling every walk “displacement 6 m” is the sign-steal.
Figure. On a straight path, position is a mark. Displacement is the arrow from the start mark to the now mark.
How it works
- Agree the line and the positive wayThe axis.
- Write start and nowThe positions.
- Name walk-length versus signed changeDistance versus displacement.
2Kinematic Equations for Motion in a Straight Line
Kinematic equations (constant acceleration on a line) link u, v, a, t, s as taught: v = u + at; s = ut + ½at²; v² = u² + 2as. They need a constant a. A jerky start-stop is not this pack.
Using v = u + at when a is not constant is a stolen formula.
Figure. Constant acceleration is a straight v–t graph. The slope is a. The intercept is u. v = u + at is that line.
How it works
- Name u, and which of a, t, s you haveThe given.
- Pick the equation that holds the unknown and the givenThe tool.
- Keep the unit (m, s, m/s, m/s²)The line-story.
u = 4 m/s, a = 2 m/s², t = 3 s
A body starts at 4 m/s and speeds up at 2 m/s² for 3 s in a straight line. Find v and s.
- v = u + at4 + 2×3 = 10 m/s
- s = ut + ½at²4×3 + ½×2×9 = 12 + 9 = 21 m
- Check v² = u² + 2as100 = 16 + 84
Pro tip. Constant a; pick the equation that holds what you need.
3Motion in a Plane
Motion in a plane is a change that needs two directions (across and up, as a sketch). A throw that goes out and up is this heading, not a second copy of the straight-line pack. At this class, name the two parts; do not invent a later-class vector dump.
A curved path photo without two named parts is a setting.
Figure. Motion in a plane splits into two perpendicular pieces. The arrow v is the pair (vx, vy), not a third mystery direction.
How it works
- Agree two axesAcross and up.
- Name the motion’s two parts as taughtThe plane-story.
- Keep each part a straight-line look if the lesson split themSchool size.
4A definition is a test you can run
Motion is a test: a change of position plus a named path (line or plane) and a named measure (distance, displacement, u, v, a). If you only say “it moved”, you have a heading.
A still photo of a car is not the test.
Figure. Distance is the path you walked. Displacement is the straight arrow from A to B. The test is: did you change the end point?
How it works
- Name start and now, or u and vThe object.
- Name the path and the measureThe test.
- Then the word has contentThe definition ran.
5Name the given before the unknown
The given are u, a, t or the two positions. The unknown is v or s (or the plane’s part). Copy the signs before you add.
Taking 4 m/s as already the finish is a silent given.
Figure. The kinematic sentence starts with what you were given. u, a and t are named before v is asked for.
How it works
- Copy u, a, t or the positionsThe given.
- Name v, s, or the part askedThe unknown.
- Then pick the equationGiven first.
6One worked case is enough at this class
One constant-a case is enough. A page of the same 4-2-3 clone does not add a new plane.
Ten twins of 21 m are still one idea.
Figure. One numerical run holds the equation: 4 plus 2 times 3 is 10. New numbers, same order.
How it works
- Run one line-case or one two-direction sketchThe case.
- A second only as a checkOptional.
- StopThis class.
7A miss: swapping the school name for the picture
A race-photo is a setting. The science is a line, signs, and a constant-a pack if a is constant. A cheer is not v.
A curved track still needs the two parts named.
Figure. Calling a number “velocity” does not make it one. Velocity is the number with a direction — the arrow, not the school word.
How it works
- Keep the race as a storyA setting.
- Write u, a, t or the two directionsThe science.
- Then compute or sketchDo not swap.
8Check by the opposite action or the opposite test
Check v by using a second kinematic equation, or check displacement by walking the signed changes back to the start. A distance that ignores the return is not the opposite test for displacement.
Adding 4+2+3 as if they were the same kind is not a check.
Figure. After v = u + at, run v^2 = u^2 + 2as on the same numbers. A check that disagrees means a given was misread.
How it works
- State 10 m/s or 21 m or 0 displacementThe claim.
- Rebuild with the other equation or the signed walkThe check.
- Mend if they disagreeHonest.
4 m forward then 4 m back has displacement
- 0 — signed change cancelled
- 8 m
- 4 m always
Distance would be 8 m; displacement is the signed change.
Notes
- Mapped to the official NCERT chapter “Describing Motion Around Us”. Original teaching only — no textbook sentences.
- Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.
Formulas
- v = u + at
- s = ut + ½at²
- v² = u² + 2as (constant a, straight line)
Recap
Hold these pegs from the official chapter “Describing Motion Around Us”. The wording is ExamMaster’s teaching, not a textbook recap.
- Motion in a Straight Line
- Straight-line motion is a change of position along one agreed line.
- Kinematic Equations for Motion in a Straight Line
- Kinematic equations (constant acceleration on a line) link u, v, a, t, s as taught: v = u + at; s = ut + ½at²; v² = u² + 2as.
- Motion in a Plane
- Motion in a plane is a change that needs two directions (across and up, as a sketch).
- A definition is a test you can run
- Motion is a test: a change of position plus a named path (line or plane) and a named measure (distance, displacement, u, v, a).
- Name the given before the unknown
- The given are u, a, t or the two positions.
- One worked case is enough at this class
- One constant-a case is enough. A page of the same 4-2-3 clone does not add a new plane.
Practise Describing Motion Around Us
Reading is free and needs no account. Practice, mocks and progress live in the app.
- A 4-question practice set that ends the chapter
- 1 quick check with worked explanations
- Timed mocks scored with the real marking scheme
- Readiness tracked per topic, kept on your device