Chapter 2- Motion in one dimension (ICSE Class 9)

ICSE Class 9 Physics Notes

Chapter 2: Motion in One Dimension

Easy notes with daily life examples, formulas, graphs, quick revision, a mini calculator, and a short self-test.

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Basic Concepts Distance & Displacement Speed & Velocity Acceleration Graphs Equations Quick Revision Self-Test

Imagine Your School Journey

Daily Life Example

Suppose every morning you travel from home to school. While travelling, you can understand almost every concept of motion.

1. Rest

A body is said to be at rest when its position does not change with time with respect to its surroundings.

Example: You are sitting in your classroom. Your position with respect to the desk, blackboard, and walls is not changing.

No change in position = Rest

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2. Motion

A body is said to be in motion when its position changes with time with respect to its surroundings.

Example: You walk from your classroom to the playground. Your position changes continuously.

Change in position = Motion

3. Linear Motion

When a body moves along a straight line path, it is called motion in one direction or linear motion.

Examples: A train on a straight track, a lift moving up and down, and a stone falling vertically.

One straight road → One-direction motion

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Distance and Displacement

Most Important

4. Distance

Distance is the total length of the path travelled by a body.

Example: Home → Shop → School. Total path travelled = 500 m. Distance = 500 m.

SI Unit: metre (m)

Distance tells us: “How much path did you travel?”

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5. Displacement

Displacement is the shortest distance between the initial and final positions in a particular direction.

Example: You walk around a park and come back to the starting point. Distance = 400 m, but displacement = 0 m.

SI Unit: metre (m)

Distance = Actual road travelled
Displacement = Shortcut distance

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Distance	Displacement
Actual path travelled	Shortest path between initial and final positions
Scalar quantity	Vector quantity
No direction	Has direction
Usually not zero during actual movement	Can be zero if initial and final positions are the same

Speed and Velocity

Formula Zone

6. Speed

Speed tells us how fast an object moves.

Speed = Distance ÷ Time

Example: A car travels 100 m in 10 s.
Speed = 100 ÷ 10 = 10 m/s

SI Unit: m/s

Speed = “How fast?”

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7. Velocity

Velocity is speed in a particular direction.

Example: A car moves at 20 m/s towards East. Here, 20 m/s is speed and East is direction.

SI Unit: m/s

Velocity = Speed + Direction

8. Average Speed

Average speed is total distance divided by total time.

Average Speed = Total Distance ÷ Total Time

Example: 60 km in 1 hour + 40 km in 1 hour = 100 km in 2 hours. Average speed = 50 km/h.

9. Instantaneous Speed

The speed at a particular instant is called instantaneous speed.

Example: The reading on a bike’s speedometer at this moment.

If speed remains constant, instantaneous speed = average speed.

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Speed	Velocity
Only magnitude	Magnitude + direction
Scalar quantity	Vector quantity
Based on distance	Based on displacement

Acceleration and Retardation

Speed Change

10. Acceleration

Acceleration means the rate of change of velocity with time.

Acceleration = Change in Velocity ÷ Time

Example: A scooter increases speed from 10 m/s to 20 m/s in 5 s.
Acceleration = (20 − 10) ÷ 5 = 2 m/s²

SI Unit: m/s²

Acceleration = Getting faster

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11. Retardation

Retardation or deceleration means decrease in velocity with time.

Example: A train slows down while approaching a station.

SI Unit: m/s²

Acceleration = Speeding up
Retardation = Slowing down

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Understanding Graphs Like a Story

Graph Reading

Imagine watching a friend running. Instead of writing numbers, we draw graphs. Graphs help us see motion at a glance.

12. Displacement-Time Graph

Body at Rest

Straight horizontal line. Position remains unchanged. Velocity = 0.

Example: A student sitting in class.

Uniform Velocity

Straight slanting line. Equal displacement takes place every second.

Example: A cyclist moving steadily.

Accelerated Motion

Curved line. Unequal displacement takes place in equal intervals of time.

Example: A bike starting from rest and changing speed.

Slope of Displacement-Time Graph = Velocity
Steeper graph → Greater velocity

13. Velocity-Time Graph

Uniform Velocity

Horizontal straight line. Velocity remains constant.

Uniform Acceleration

Straight line rising upward. Velocity increases uniformly.

Uniform Retardation

Straight line sloping downward. Velocity decreases uniformly.

Area under Velocity-Time Graph = Displacement

14. Acceleration-Time Graph

Uniform Acceleration

Horizontal straight line. Acceleration remains constant.

Zero Acceleration

Graph lies on the time axis. Velocity is not changing.

Three Equations of Motion

Uniform Acceleration

These equations are applicable only when acceleration is uniform.

First Equation

Think: Final velocity = Initial velocity + Extra velocity gained

v = u + at

Future = Present + Gain

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Second Equation

Think: Distance travelled after moving for some time.

s = ut + 1/2 at²

Distance = Motion due to speed + Motion due to acceleration

Third Equation

Think: Used when time is not given.

v² − u² = 2as

No time? Use the third equation.

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Interactive Motion Calculator

Practice Tool

Speed Calculator

Distance Time

Result will appear here.

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Acceleration Calculator

Initial Velocity (u) Final Velocity (v) Time (t)

Result will appear here.

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Super Quick Revision

Exam Ready

Standing bike
Rest

Moving bike
Motion

Total road travelled
Distance

Shortcut from start to finish
Displacement

How fast?
Speed

How fast + direction?
Velocity

Speed increasing
Acceleration

Speed decreasing
Retardation

Slope of Displacement-Time Graph
Velocity

Slope of Velocity-Time Graph
Acceleration

Area under Velocity-Time Graph
Displacement

Equations of Motion
Only for uniform acceleration

This “bike journey” is enough to remember the entire Motion in One Dimension chapter for ICSE Class 9.

Quick Self-Test

Check Yourself

1. What is velocity?

2. What does the slope of a displacement-time graph give?

3. Which equation is useful when time is not given?

Choose an answer to check.

Check Out More

Related Lessons

Motion with Story Book and Test Graphs with Story Book and Test Graphs Equations of Motion

Frequently Asked Questions

FAQs

What is motion in one dimension?

Motion in one dimension means motion along a straight line, such as a lift moving up and down or a train moving on a straight track.

What is the difference between distance and displacement?

Distance is the total path travelled. Displacement is the shortest distance between the starting point and ending point in a particular direction.

What is the difference between speed and velocity?

Speed tells how fast an object moves. Velocity tells how fast an object moves in a particular direction.

What does acceleration mean?

Acceleration means the rate of change of velocity with time. If velocity increases, the body is accelerating.

When are the three equations of motion used?

The three equations of motion are used only when acceleration is uniform.

What does the area under a velocity-time graph represent?

The area under a velocity-time graph represents displacement.

Made by Shaleen Shekhar

For ICSE Class 9 Physics learners | Speed Up Science