Chapter 1: Motion
Comprehensive Study Notes & Fundamentals
1. Motion
An object is said to be in motion if it changes its position with time with respect to a reference point.
Examples:
• A car moving on a road → Motion
• A book on a table → At rest
Key Concept: Motion is always relative. An object can be at rest relative to one frame of reference
while in motion relative to another.
2. Distance and Displacement
Distance
• It is the total path length covered by an object during its journey.
• It is a scalar quantity (has magnitude only, no direction).
• It is always positive.
• SI Unit: meter (m)
Displacement
• It is the shortest distance measured between the initial position and the final position of an object.
• It is a vector quantity (has both magnitude and direction).
• It can be zero, positive, or negative.
• SI Unit: meter (m)
Class 9 Physics • Chapter 1: Motion Page 1 of 5
, Comparison Profile
S.No. Distance Displacement
Shortest path between initial and final
1 Total path covered by an object.
positions.
2 Scalar quantity. Vector quantity.
3 Always positive. Can be positive, negative, or zero.
Illustrative Example:
If a person walks 5 m forward and then 5 m back to the starting position:
• Distance Covered: 5 m + 5 m = 10 m
• Total Displacement: 5 m - 5 m = 0 m (since the initial and final points are identical)
3. Speed
Speed is defined as the distance covered per unit time.
Speed = ——————
Distance
Time
• SI Unit: meters per second (m/s)
Types of Speed:
1. Uniform Speed: When an object covers equal distances in equal intervals of time.
2. Non-Uniform Speed: When an object covers unequal distances in equal intervals of time.
3. Average Speed: The total distance traveled divided by the total time taken.
Average Speed = —————————
Total Distance
Total Time
4. Velocity
Velocity is defined as the displacement per unit time.
Class 9 Physics • Chapter 1: Motion Page 2 of 5
Comprehensive Study Notes & Fundamentals
1. Motion
An object is said to be in motion if it changes its position with time with respect to a reference point.
Examples:
• A car moving on a road → Motion
• A book on a table → At rest
Key Concept: Motion is always relative. An object can be at rest relative to one frame of reference
while in motion relative to another.
2. Distance and Displacement
Distance
• It is the total path length covered by an object during its journey.
• It is a scalar quantity (has magnitude only, no direction).
• It is always positive.
• SI Unit: meter (m)
Displacement
• It is the shortest distance measured between the initial position and the final position of an object.
• It is a vector quantity (has both magnitude and direction).
• It can be zero, positive, or negative.
• SI Unit: meter (m)
Class 9 Physics • Chapter 1: Motion Page 1 of 5
, Comparison Profile
S.No. Distance Displacement
Shortest path between initial and final
1 Total path covered by an object.
positions.
2 Scalar quantity. Vector quantity.
3 Always positive. Can be positive, negative, or zero.
Illustrative Example:
If a person walks 5 m forward and then 5 m back to the starting position:
• Distance Covered: 5 m + 5 m = 10 m
• Total Displacement: 5 m - 5 m = 0 m (since the initial and final points are identical)
3. Speed
Speed is defined as the distance covered per unit time.
Speed = ——————
Distance
Time
• SI Unit: meters per second (m/s)
Types of Speed:
1. Uniform Speed: When an object covers equal distances in equal intervals of time.
2. Non-Uniform Speed: When an object covers unequal distances in equal intervals of time.
3. Average Speed: The total distance traveled divided by the total time taken.
Average Speed = —————————
Total Distance
Total Time
4. Velocity
Velocity is defined as the displacement per unit time.
Class 9 Physics • Chapter 1: Motion Page 2 of 5
