Motion Class 9 CBSE Notes - Chapter 8
Click on the link below to access the NCERT Solutions for Class 9 Science Chapter 8 Motion.
Class 9 Science Chapter 8 Motion
In Class 9 Science Chapter 8 Motion, students learn to describe the motion of objects along a straight line
and express such motions through simple equations and graphs. The chapter also discusses ways of
describing circular motion.
Understanding Motion
Reference point and reference frame
● To describe the position of an object we need a reference point or origin. An object may seem to be
moving to one observer and stationary to another.
● Example: A passenger inside a bus sees the other passengers to be at rest, whereas an observer
outside the bus sees the passengers to be in motion.
● In order to make observations easy, a convention or a common reference point or frame is needed.
All objects must be in the same reference frame
To know more about the frame of reference, visit here.
Distance and Displacement
The magnitude of the length covered by a moving object is called distance. It has no direction.
Displacement is the shortest distance between two points or the distance between the starting and final
positions with respect to time. It has magnitude as well as direction.
Displacement can be zero, but distance cannot.
To know more about Distance and Displacement, visit here.
, Magnitude
Magnitude is the size or extent of a physical quantity. In physics, we have scalar and vector quantities.
Scalar quantities are only expressed as magnitude. E.g: time, distance, mass, temperature, area, volume
Vector quantities are expressed in magnitude as well as the direction of the object. E.g: Velocity,
displacement, weight, momentum, force, acceleration, etc.
Time, Average Speed and Velocity
Time and speed
Time is the duration of an event that is expressed in seconds. Most physical phenomena occur with respect
to time. It is a scalar quantity.
Speed is the rate of change of distance. If a body covers a certain distance in a certain amount of time, its
speed is given by
The instantaneous speed is the speed of an object at a particular moment in time.
Average speed is stated as the distance covered by the object within a period of time.
Average speed = Total distance travelled / Total time taken
The below table lists the difference between Average Speed and Instantaneous Speed.
Average Speed Instantaneous Speed
It is defined as the total distance travelled It is defined as the speed at a particular
divided by the total time elapsed. instant of time.
It is constant It is not constant
Click on the link below to access the NCERT Solutions for Class 9 Science Chapter 8 Motion.
Class 9 Science Chapter 8 Motion
In Class 9 Science Chapter 8 Motion, students learn to describe the motion of objects along a straight line
and express such motions through simple equations and graphs. The chapter also discusses ways of
describing circular motion.
Understanding Motion
Reference point and reference frame
● To describe the position of an object we need a reference point or origin. An object may seem to be
moving to one observer and stationary to another.
● Example: A passenger inside a bus sees the other passengers to be at rest, whereas an observer
outside the bus sees the passengers to be in motion.
● In order to make observations easy, a convention or a common reference point or frame is needed.
All objects must be in the same reference frame
To know more about the frame of reference, visit here.
Distance and Displacement
The magnitude of the length covered by a moving object is called distance. It has no direction.
Displacement is the shortest distance between two points or the distance between the starting and final
positions with respect to time. It has magnitude as well as direction.
Displacement can be zero, but distance cannot.
To know more about Distance and Displacement, visit here.
, Magnitude
Magnitude is the size or extent of a physical quantity. In physics, we have scalar and vector quantities.
Scalar quantities are only expressed as magnitude. E.g: time, distance, mass, temperature, area, volume
Vector quantities are expressed in magnitude as well as the direction of the object. E.g: Velocity,
displacement, weight, momentum, force, acceleration, etc.
Time, Average Speed and Velocity
Time and speed
Time is the duration of an event that is expressed in seconds. Most physical phenomena occur with respect
to time. It is a scalar quantity.
Speed is the rate of change of distance. If a body covers a certain distance in a certain amount of time, its
speed is given by
The instantaneous speed is the speed of an object at a particular moment in time.
Average speed is stated as the distance covered by the object within a period of time.
Average speed = Total distance travelled / Total time taken
The below table lists the difference between Average Speed and Instantaneous Speed.
Average Speed Instantaneous Speed
It is defined as the total distance travelled It is defined as the speed at a particular
divided by the total time elapsed. instant of time.
It is constant It is not constant
