Class 9 Science – Describing Motion Around Us | Original Visual Revision Notes

📝 Section 1 — Classroom Notes

Have you ever noticed that when you are sitting in a moving train, the trees seem to fly past you — but the person sitting next to you seems perfectly still? This is because motion is relative. Whether something is "moving" or "at rest" depends entirely on what you compare it to. This simple idea is the foundation of everything we study in this chapter.

Scientists describe motion using numbers — distance, speed, velocity, and acceleration. Just like a cricket commentator describes a ball's speed in km/h, scientists use precise measurements and equations to describe exactly how fast, how far, and in which direction an object is moving. These numbers let us predict where a rocket will land, how long a journey takes, and why a car needs a safe braking distance.

In this chapter, we will learn the three famous equations of motion, understand position-time and velocity-time graphs, and explore what happens when objects move in circles. By the end, you will be able to calculate the speed of a running cheetah, the acceleration of a sports car, and the distance covered by a falling stone — all with simple maths!

🚶 Topic 1: What is Motion?

When a thing changes its place, it moves.
This change of place is called motion.
If a thing stays at the same spot, it is at rest.
We need a fixed point to tell if something moved.
This fixed point is called a reference point.

📏 Topic 2: Reference Point and Position

A reference point is a starting mark.
We measure how far a thing is from it.
The place of the thing is its position.
Position tells the distance and the direction.
We use plus or minus for direction.

👣 Topic 3: Distance and Displacement

Distance is the total path you walk.
Displacement is the shortest path from start to end.
Distance is always positive (never zero unless you stay).
Displacement can be positive, negative, or zero.
Displacement is always equal to or less than distance.

⏰ Topic 4: Average Speed

Speed tells how fast a thing moves.
Average speed = total distance ÷ total time.
The SI unit of speed is m/s (metre per second).
Speed has no direction (just a number).
Equal distances in equal times = uniform speed.

🎯 Topic 5: Average Velocity

Velocity = displacement ÷ time.
Velocity has both size and direction.
Its SI unit is also m/s.
Velocity can be positive or negative.
Speed and velocity are different things.

🚀 Topic 6: Acceleration

Acceleration = change in velocity ÷ time.
It tells how quickly velocity changes.
Its SI unit is m/s².
Positive acceleration = speeding up.
Negative acceleration = slowing down.

📐 Topic 7: Equations of Motion

Equation 1: v = u + at (find final speed).
Equation 2: s = ut + ½at² (find distance).
Equation 3: v² = u² + 2as (no time needed).
u = initial velocity, v = final velocity.
These work only when acceleration is constant.

📈 Topic 8: Position-Time Graphs

Time goes on the X-axis (horizontal).
Position goes on the Y-axis (vertical).
A straight line = constant speed.
A curved line = changing speed.
A flat line = the thing is not moving.

📊 Topic 9: Velocity-Time Graphs

Time on X-axis, velocity on Y-axis.
A flat line = constant velocity (no acceleration).
A rising line = velocity is going up.
The slope of the line gives acceleration.
The area under the line gives displacement.

🔄 Topic 10: Uniform Circular Motion

Moving in a circle at the same speed.
The speed stays the same but direction changes.
So the velocity keeps changing.
One full round = distance is 2πR.
One full round = displacement is zero.

✏️ Section 3 — Worked Examples

💡 Example 1: Finding Average Speed and Average Velocity

A boy walks 80 m east, then turns and walks 30 m west. He takes 55 s in total. Find his average speed and average velocity.

Write what we know.
Total distance = 80 m + 30 m = 110 m.
Displacement = 80 m − 30 m = 50 m east.
Time = 55 s.

Find average speed.
Average speed = total distance ÷ time
= 110 m ÷ 55 s = 2 m/s.

Find average velocity.
Average velocity = displacement ÷ time
= 50 m ÷ 55 s ≈ 0.91 m/s east.

✔ Average speed = 2 m/s. Average velocity ≈ 0.91 m/s east.

💡 Example 2: Using Equations of Motion

A scooter starts from rest and speeds up at 3 m/s² for 8 seconds. Find the final velocity and the distance covered.

Write what we know.
u = 0 m/s (starts from rest), a = 3 m/s², t = 8 s.

Find final velocity using Equation 1.
v = u + at
v = 0 + 3 × 8 = 24 m/s.

Find distance using Equation 2.
s = ut + ½at²
s = 0 × 8 + ½ × 3 × 8²
s = 0 + ½ × 3 × 64 = 96 m.

✔ Final velocity = 24 m/s. Distance covered = 96 m.

💡 Example 3: Braking Distance

A car moves at 72 km/h and brakes are applied. The acceleration is −5 m/s². How far does it go before stopping?

Convert speed to m/s.
72 km/h = 72 × 1000 ÷ 3600 = 20 m/s.

Write what we know.
u = 20 m/s, v = 0 m/s (stops), a = −5 m/s².

Use Equation 3 to find distance.
v² = u² + 2as
0 = (20)² + 2 × (−5) × s
0 = 400 − 10s
10s = 400
s = 40 m.

✔ The car travels 40 m before stopping.

📋 Section 4 — Cheat Sheet

Term	Meaning	Unit / Note
Motion	Change in position over time	—
Rest	Position does not change	—
Reference point	Fixed point to measure from	Also called origin
Distance	Total path length	m (always positive)
Displacement	Shortest path from start to end	m (has direction)
Average speed	Distance ÷ time	m/s (no direction)
Average velocity	Displacement ÷ time	m/s (has direction)
Acceleration	Change in velocity ÷ time	m/s²
Uniform motion	Equal distances in equal times	Speed is constant
Position-time graph	Shows position vs time	Slope = velocity
Velocity-time graph	Shows velocity vs time	Slope = acceleration, Area = displacement
Equation 1	v = u + at	Finds final velocity
Equation 2	s = ut + ½at²	Finds displacement
Equation 3	v² = u² + 2as	No time needed
Uniform circular motion	Same speed in a circle	Direction always changes

💭 Remember: Speed has no direction. Velocity has direction. Acceleration tells how fast velocity changes.

🏠 Section 5 — Take-Home Handout

✏️ Part A: Fill in the Blanks

1. The change in position of a thing is called ________.
2. Distance is always ________ or positive.
3. Displacement can be positive, negative, or ________.
4. Average speed = total ________ ÷ total time.
5. The SI unit of acceleration is ________.
6. In uniform motion, an object covers ________ distances in equal times.
7. On a position-time graph, the slope gives the ________.
8. On a velocity-time graph, the area under the line gives ________.
9. The first equation of motion is v = u + ________.
10. In uniform circular motion, speed is ________ but direction changes.

✅ Part B: True or False

1. Distance can be negative. ( ______ )
2. Displacement can be zero even if distance is not zero. ( ______ )
3. Speed and velocity are always the same. ( ______ )
4. Negative acceleration means slowing down. ( ______ )
5. A flat line on a position-time graph means the thing is moving fast. ( ______ )

🔢 Part C: Solve These

C1. A cyclist goes 150 m in 30 s. What is the average speed?

C2. A bus starts from rest and reaches 18 m/s in 6 s. What is the acceleration?

C3. A van moves at 90 km/h. Convert this speed to m/s.

🔗 Part D: Match the Columns

Column A	Column B
1. Distance	a. Displacement ÷ time
2. Average velocity	b. Total path length
3. Acceleration	c. v = u + at
4. Equation 1	d. Change in velocity ÷ time
5. Uniform circular motion	e. Same speed, changing direction

Answers: 1–____, 2–____, 3–____, 4–____, 5–____

🎨 Part E: Draw and Label

Draw a velocity-time graph for a car that:

Starts at 0 m/s.
Speeds up at constant acceleration for 6 s.
Reaches 12 m/s at t = 6 s.

Label the axes (time, velocity) and mark the points.

✅ Detailed Solutions — Section 5 Take-Home Handout

Part A — Fill in the Blanks (Answers)

The change in position of a thing is called motion.
Distance is always zero or positive — it can never be negative because it is total path length.
Displacement can be positive, negative, or zero. (Zero when you return to your starting point.)
Average speed = total distance ÷ total time.
The SI unit of acceleration is m/s² (metres per second squared).
In uniform motion, an object covers equal distances in equal times.
On a position-time graph, the slope gives the velocity (speed with direction).
On a velocity-time graph, the area under the line gives displacement.
The first equation of motion is v = u + at.
In uniform circular motion, speed is constant but direction keeps changing.

Part B — True or False (Answers)

False. Distance can never be negative. It is total path length, always zero or positive.
True. Walk in a circle and return to start: displacement = 0, distance = full circle length.
False. Speed and velocity are NOT always the same. Speed has no direction; velocity has direction.
True. Negative acceleration (deceleration) means velocity is decreasing — the object is slowing down.
False. A flat horizontal line means position is NOT changing — the object is at rest.

Part C — Solve (Step-by-Step)

C1. Cyclist goes 150 m in 30 s. Average speed?

1Formula: Speed = Distance ÷ Time

2= 150 ÷ 30 = 5

✔ Average speed = 5 m/s

C2. Bus starts from rest, reaches 18 m/s in 6 s. Acceleration?

1Formula: a = (v − u) ÷ t

2a = (18 − 0) ÷ 6 = 18 ÷ 6 = 3

✔ Acceleration = 3 m/s²

C3. Van moves at 90 km/h. Convert to m/s.

1Rule: divide km/h by 3.6 to get m/s

2= 90 ÷ 3.6 = 25

✔ Speed = 25 m/s

Part D — Match the Columns (Answers)

Distance → b. Total path length
Average velocity → a. Displacement ÷ time
Acceleration → d. Change in velocity ÷ time
Equation 1 → c. v = u + at
Uniform circular motion → e. Same speed, changing direction

Part E — Velocity-Time Graph (Guidance)

X-axis: Time (s) from 0 to 6. Y-axis: Velocity (m/s) from 0 to 12.
Plot point (0, 0) and point (6, 12). Connect with a straight line.
Slope = acceleration = 12 ÷ 6 = 2 m/s².
Area under line (triangle) = ½ × 6 × 12 = 36 m (displacement).

🃏 Section 6 — Revision Flashcards

Light side = Question. Dark side = Answer.

Q1: What is motion?

A1: Change in position of a thing over time.

Q2: What is the difference between distance and displacement?

A2: Distance = total path. Displacement = shortest path from start to end with direction.

Q3: What is average speed?

A3: Total distance divided by total time. No direction. Unit: m/s.

Q4: What is acceleration?

A4: Change in velocity divided by time. Unit: m/s².

Q5: Write the three equations of motion.

A5: v = u + at, s = ut + ½at², v² = u² + 2as.

Q6: What does the slope of a position-time graph tell us?

A6: It tells us the velocity (speed with direction).

Q7: What does the area under a velocity-time graph tell us?

A7: It tells us the displacement (distance in one direction).

Q8: What is uniform circular motion?

A8: Moving in a circle at constant speed. Speed stays the same but direction keeps changing.

🚗 Class 9 Science – Describing Motion Around Us
Original Visual Revision Notes Aligned with the Class 9 Science syllabus. Independently created study material. Not affiliated with or endorsed by NCERT.

📖 What is Inside

📝 Section 1 — Classroom Notes

🚶 Topic 1: What is Motion?

📏 Topic 2: Reference Point and Position

👣 Topic 3: Distance and Displacement

⏰ Topic 4: Average Speed

🎯 Topic 5: Average Velocity

🚀 Topic 6: Acceleration

📐 Topic 7: Equations of Motion

📈 Topic 8: Position-Time Graphs

📊 Topic 9: Velocity-Time Graphs

🔄 Topic 10: Uniform Circular Motion

🎨 Section 2 — Easy Illustrations

✏️ Section 3 — Worked Examples

💡 Example 1: Finding Average Speed and Average Velocity

💡 Example 2: Using Equations of Motion

💡 Example 3: Braking Distance

📋 Section 4 — Cheat Sheet

🏠 Section 5 — Take-Home Handout

✏️ Part A: Fill in the Blanks

✅ Part B: True or False

🔢 Part C: Solve These

🔗 Part D: Match the Columns

🎨 Part E: Draw and Label

✅ Detailed Solutions — Section 5 Take-Home Handout

Part A — Fill in the Blanks (Answers)

Part B — True or False (Answers)

Part C — Solve (Step-by-Step)

Part D — Match the Columns (Answers)

Part E — Velocity-Time Graph (Guidance)

🃏 Section 6 — Revision Flashcards

🧠 Section 7 — Mind Map

🚗 Class 9 Science – Describing Motion Around UsOriginal Visual Revision Notes Aligned with the Class 9 Science syllabus. Independently created study material. Not affiliated with or endorsed by NCERT.

📖 What is Inside

📝 Section 1 — Classroom Notes

🚶 Topic 1: What is Motion?

📏 Topic 2: Reference Point and Position

👣 Topic 3: Distance and Displacement

⏰ Topic 4: Average Speed

🎯 Topic 5: Average Velocity

🚀 Topic 6: Acceleration

📐 Topic 7: Equations of Motion

📈 Topic 8: Position-Time Graphs

📊 Topic 9: Velocity-Time Graphs

🔄 Topic 10: Uniform Circular Motion

🎨 Section 2 — Easy Illustrations

✏️ Section 3 — Worked Examples

💡 Example 1: Finding Average Speed and Average Velocity

💡 Example 2: Using Equations of Motion

💡 Example 3: Braking Distance

📋 Section 4 — Cheat Sheet

🏠 Section 5 — Take-Home Handout

✏️ Part A: Fill in the Blanks

✅ Part B: True or False

🔢 Part C: Solve These

🔗 Part D: Match the Columns

🎨 Part E: Draw and Label

✅ Detailed Solutions — Section 5 Take-Home Handout

Part A — Fill in the Blanks (Answers)

Part B — True or False (Answers)

Part C — Solve (Step-by-Step)

Part D — Match the Columns (Answers)

Part E — Velocity-Time Graph (Guidance)

🃏 Section 6 — Revision Flashcards

🧠 Section 7 — Mind Map

🚗 Class 9 Science – Describing Motion Around Us
Original Visual Revision Notes Aligned with the Class 9 Science syllabus. Independently created study material. Not affiliated with or endorsed by NCERT.