Chapter 2- Motion in one dimension
(ICSE Class 9) – Easy Notes with Daily
Life Examples
Imagine Your School Journey
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.
Therefore, you are at rest.
Key Idea
No change in position = Rest
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.
Therefore, you are in motion.
Key Idea
Change in position = Motion
3. Motion in One Direction (Linear Motion)
When a body moves along a straight line path, it is called motion in one direction.
Examples
A train moving on a straight track.
A lift moving up and down.
A stone falling vertically.
Easy Memory Trick
One straight road → One-direction motion
4. Distance
Distance is the total length of the path travelled by a body.
Example
Suppose you walk:
Home → Shop → School
Total path travelled = 500 m
Distance = 500 m
Key Point
Distance tells us:
"How much path did you travel?"
SI Unit
metre (m)
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 travelled = 400 m
Displacement = 0 m
Why?
Because your starting and ending points are the same.
Easy Memory Trick
Distance = Actual road travelled
Displacement = Shortcut distance
SI Unit
metre (m)
Difference Between Distance and Displacement
Distance
1.Actual path
2.Scalar quantity
3.No direction
4.Never zero during motion
Displacement
1.Shortest path
2.Vector quantity
3.Has direction
4.Can be zero
6. Speed
Speed tells us how fast an object moves.
Formula
Speed = Distance ÷ Time
Example
A car travels 100 m in 10 s.
Speed = 100 ÷ 10
= 10 m/s
Easy Memory Trick
Speed = "How fast?"
SI Unit
m/s
7. Velocity
Velocity is speed in a particular direction.
Example
A car moves at 20 m/s towards East.
Here,
20 m/s = Speed
East = Direction
Therefore it is Velocity.
Easy Memory Trick
Velocity = Speed + Direction
SI Unit
m/s
Difference Between Speed and Velocity
Speed
1.Only magnitude
2.Scalar
3.Distance based
Velocity
1.Magnitude + direction
2.Vector
3.Displacement based
8. Average Speed
Average Speed = Total Distance ÷ Total Time
Example
You travel:
60 km in 1 hour
40 km in 1 hour
Total Distance = 100 km
Total Time = 2 h
Average Speed = 100 ÷ 2
= 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.
Interesting Fact
When speed remains constant throughout the journey,
Instantaneous Speed = Average Speed
10. Acceleration
Acceleration means increase in velocity every second.
Formula
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
Easy Memory Trick
Acceleration = Getting faster
SI Unit
m/s²
11. Retardation (Deceleration)
Retardation means decrease in velocity every second.
Example
A train slows down while approaching a station.
Easy Memory Trick
Acceleration = Speeding up
Retardation = Slowing down
SI Unit
m/s²
Understanding Graphs Like a Story
Imagine watching a friend running.
Instead of writing numbers, we draw graphs.
Graphs help us see motion at a glance.
12. Displacement-Time Graph
Case 1: Body at Rest
Straight horizontal line.
Position remains unchanged.
Velocity = 0
Example
A student sitting in class.
Case 2: Uniform Velocity
Straight slanting line.
Equal displacement every second.
Example
A cyclist moving steadily.
Case 3: Accelerated Motion
Curved line.
Unequal Displacement
Example
A bike starting from rest and gaining and reducing speed.
Important Point
Slope of Displacement-Time Graph = Velocity
Easy Memory Trick
Steeper graph → Greater velocity
13. Velocity-Time Graph
Case 1: Uniform Velocity
Horizontal straight line.
Velocity remains constant.
Case 2: Uniform Acceleration
Straight line rising upward.
Velocity increases uniformly.
Case 3: Uniform Retardation
Straight line sloping downward.
Velocity decreases uniformly.
Most Important Concept
Area under Velocity-Time Graph = Displacement
Easy Memory Trick
Area under graph = Distance travelled in a direction
14. Acceleration-Time Graph
Uniform Acceleration
Horizontal straight line.
(Acceleration remains constant.)
Zero Acceleration
Graph lies on time axis.
Velocity is not changing.
Three Equations of Motion
Applicable only when acceleration is uniform.
First Equation of Motion
Think:
Final Velocity = Initial Velocity + Extra Velocity Gained
v= u + at
Memory Trick
Future = Present + Gain
Second Equation of Motion
Think:
Distance travelled after moving for some time.
s = ut + 1/2 at²
Memory Trick
Distance = Motion due to speed + Motion due to acceleration
Third Equation of Motion
Think:
Used when time is not given.
2as = v² - u²
Memory Trick
No time?
Super Quick Revision
Imagine a bike ride:
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
Three Equations of Motion work only for uniform acceleration.
So. This "bike journey" is enough to remember the entire Motion in one dimension chapter for ICSE Class 9.
