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ATP EducationScience Exploration Notes Class 9 English Medium 2026-27
Science Exploration Notes Class 9 English Medium 2026-27 now available for students studying in cbse school, up board, state boards and international cbse schools and Latest CBSE Curriculum based on NCERT books.
Science Exploration Notes Class 9 English Medium 2026-27
All topics of Chapter 4
1. Chapter Review and Key Points 2. Motion in a Straight Line 3. Measuring Motion 4. Types of Motion 5. Graphical Representation of Motion 6. Assignments - What Have You Learned?Science Exploration Chapter 4. Describing Motion Around Us
CBSE Notes New Syllabus: Class 9
Assignments - What Have You Learned?
Chapter 4. Describing Motion Around Us
This section explains the concepts of distance, displacement, average speed, average velocity and acceleration. These physical quantities help us describe motion accurately and compare the movement of different objects.
9. Distance Travelled
Whenever an object moves, it covers a certain path. The total length of this actual path is called the distance travelled. Distance depends only on the path followed and not on the direction of motion.
Definition
Distance is the total length of the actual path travelled by an object between two points.
Characteristics
- Scalar Quantity – It has only magnitude.
- No Direction – Direction is not considered.
- Always Positive – Distance can never be negative.
- Depends on Path – Different paths may have different distances.
SI Unit
The SI unit of distance is metre (m).
10. Displacement
Displacement represents the shortest straight-line distance between the initial and final positions of an object. Unlike distance, it also specifies the direction of motion.
Definition
Displacement is the shortest distance between the initial and final positions of an object in a specified direction.
Characteristics
- Vector Quantity – It has both magnitude and direction.
- Shortest Distance – Always the minimum possible distance.
- May be Zero – If an object returns to its starting point, displacement becomes zero.
- Independent of Path – Depends only on the initial and final positions.
SI Unit
The SI unit of displacement is metre (m).
11. Difference Between Distance and Displacement
| Distance | Displacement |
|---|---|
| Total length of the actual path travelled. | Shortest distance between two positions. |
| Scalar quantity. | Vector quantity. |
| No direction. | Direction is essential. |
| Always positive. | May be positive, negative or zero. |
| Depends on the path followed. | Depends only on initial and final positions. |
12. Speed
Speed tells us how fast an object moves. It is one of the most commonly used quantities to describe motion.
Definition
Speed is the distance travelled by an object per unit time.
Formula
Speed = Distance ÷ Time
SI Unit
The SI unit of speed is metre per second (m/s).
Other Unit
Kilometre per hour (km/h) is commonly used for vehicles.
13. Average Speed
An object may move at different speeds during a journey. Therefore, we calculate the average speed for the entire journey.
Definition
Average speed is the total distance travelled divided by the total time taken.
Formula
Average Speed = Total Distance Travelled ÷ Total Time Taken
Important Points
- Scalar Quantity – Has only magnitude.
- Based on Distance – Uses the total path travelled.
- Always Positive – Cannot have a negative value.
14. Velocity
Velocity describes both the speed and the direction of motion. Two objects may have the same speed but different velocities if they move in different directions.
Definition
Velocity is the displacement of an object per unit time in a specified direction.
Formula
Velocity = Displacement ÷ Time
Characteristics
- Vector Quantity – Has magnitude and direction.
- Depends on Displacement – Not on the total path.
- May be Positive or Negative – Depends on the direction of motion.
15. Difference Between Speed and Velocity
| Speed | Velocity |
|---|---|
| Based on distance. | Based on displacement. |
| Scalar quantity. | Vector quantity. |
| No direction. | Direction is necessary. |
| Always positive. | May be positive, negative or zero. |
16. Average Velocity
When the velocity of an object changes during motion, the average velocity gives the overall rate of displacement.
Definition
Average velocity is the total displacement divided by the total time taken.
Formula
Average Velocity = Total Displacement ÷ Total Time Taken
17. Acceleration
Sometimes an object speeds up, slows down or changes its direction. Such changes indicate acceleration.
Definition
Acceleration is the rate of change of velocity with respect to time.
Formula
Acceleration = Change in Velocity ÷ Time Taken
SI Unit
The SI unit of acceleration is metre per second squared (m/s²).
Types of Acceleration
- Positive Acceleration – Velocity increases with time.
- Negative Acceleration (Retardation) – Velocity decreases with time.
- Zero Acceleration – Velocity remains constant.
ATP Education Tip
For CBSE examinations, remember these four formulas: Speed = Distance ÷ Time, Average Speed = Total Distance ÷ Total Time, Velocity = Displacement ÷ Time, and Acceleration = Change in Velocity ÷ Time. Also remember that Distance & Speed are scalar quantities, whereas Displacement, Velocity and Acceleration are vector quantities.