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# Chapter 8 Motion Class 9 Notes | EduRev

## Class 9 : Chapter 8 Motion Class 9 Notes | EduRev

``` Page 1

Chapter 8 Motion
Motion – An object that changes its position with respect to time is known to be in motion.
Rest – An object is said to be at rest when it does not change its position with respect to time.
A reference point is required to describe a motion.
For e.g.
1. A car is moving at 60km/hr. It means that the car is moving with respect to its surrounding. The
reference point here is the surrounding.
2. A person travelling by a bus. The bus and the person are in motion with respect to the surrounding i.e.
the plants, trees road etc. The reference points here are the surroundings.
But the person and the bus are at rest with each other because they are moving at same speed and the
man always remain at one point inside the bus. The reference point in this case is the bus for the man
and vice-a-versa.

Motion is a straight line
Describing the motion in a straight line –
The point from where an object stars moving is treated as its reference point.
Distance – the total path length covered by the object from its reference point. Distance only has magnitude
(magnitude = numerical value)
Displacement – The shortest distance covered by an object from its reference point. Displacement has both
magnitude and direction.
The shortest distance is always a straight line dram from the reference point to the point of end
of the motion.

E.g.
O    A    B     C

0              20    40    60 km

Consider an object moves from point O to C and then comes back to point A
Distance covered by the object will be = OC + CA
= 60 + 40
= 100 km
And
Displacement = Shortest distance from the reference point i.e. point O to the end point of end of motion i.e.
point A, which is OA
Page 2

Chapter 8 Motion
Motion – An object that changes its position with respect to time is known to be in motion.
Rest – An object is said to be at rest when it does not change its position with respect to time.
A reference point is required to describe a motion.
For e.g.
1. A car is moving at 60km/hr. It means that the car is moving with respect to its surrounding. The
reference point here is the surrounding.
2. A person travelling by a bus. The bus and the person are in motion with respect to the surrounding i.e.
the plants, trees road etc. The reference points here are the surroundings.
But the person and the bus are at rest with each other because they are moving at same speed and the
man always remain at one point inside the bus. The reference point in this case is the bus for the man
and vice-a-versa.

Motion is a straight line
Describing the motion in a straight line –
The point from where an object stars moving is treated as its reference point.
Distance – the total path length covered by the object from its reference point. Distance only has magnitude
(magnitude = numerical value)
Displacement – The shortest distance covered by an object from its reference point. Displacement has both
magnitude and direction.
The shortest distance is always a straight line dram from the reference point to the point of end
of the motion.

E.g.
O    A    B     C

0              20    40    60 km

Consider an object moves from point O to C and then comes back to point A
Distance covered by the object will be = OC + CA
= 60 + 40
= 100 km
And
Displacement = Shortest distance from the reference point i.e. point O to the end point of end of motion i.e.
point A, which is OA
Hence, displacement = OA = 20km to the right or west of the reference point
Magnitude  Direction
Uniform motion – An object is said to be in uniform motion when it covers equal distances in equal interval of
times. For e.g. A car covered 40km in each hour.
Graph for Uniform motion
Time  (hr) Distance (km)
1 40
2 80
3 120
4 160
5 200
6 240
7 280

Graph 1 – Uniform motion
Non – uniform motion – An object is said to be in non-uniform motion when it covers unequal distance in
equal intervals of time. For e.g. a man walking in a park.
Graph of Non-uniform motion
Time
(hr) Distance (km)
1 10
2 15
3 17
4 30
5 45
6 80
7 90

1, 40
2, 80
3, 120
4, 160
5, 200
6, 240
7, 280
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7 8
Distance (km)
TIme (hr)
Distance vs Time
Page 3

Chapter 8 Motion
Motion – An object that changes its position with respect to time is known to be in motion.
Rest – An object is said to be at rest when it does not change its position with respect to time.
A reference point is required to describe a motion.
For e.g.
1. A car is moving at 60km/hr. It means that the car is moving with respect to its surrounding. The
reference point here is the surrounding.
2. A person travelling by a bus. The bus and the person are in motion with respect to the surrounding i.e.
the plants, trees road etc. The reference points here are the surroundings.
But the person and the bus are at rest with each other because they are moving at same speed and the
man always remain at one point inside the bus. The reference point in this case is the bus for the man
and vice-a-versa.

Motion is a straight line
Describing the motion in a straight line –
The point from where an object stars moving is treated as its reference point.
Distance – the total path length covered by the object from its reference point. Distance only has magnitude
(magnitude = numerical value)
Displacement – The shortest distance covered by an object from its reference point. Displacement has both
magnitude and direction.
The shortest distance is always a straight line dram from the reference point to the point of end
of the motion.

E.g.
O    A    B     C

0              20    40    60 km

Consider an object moves from point O to C and then comes back to point A
Distance covered by the object will be = OC + CA
= 60 + 40
= 100 km
And
Displacement = Shortest distance from the reference point i.e. point O to the end point of end of motion i.e.
point A, which is OA
Hence, displacement = OA = 20km to the right or west of the reference point
Magnitude  Direction
Uniform motion – An object is said to be in uniform motion when it covers equal distances in equal interval of
times. For e.g. A car covered 40km in each hour.
Graph for Uniform motion
Time  (hr) Distance (km)
1 40
2 80
3 120
4 160
5 200
6 240
7 280

Graph 1 – Uniform motion
Non – uniform motion – An object is said to be in non-uniform motion when it covers unequal distance in
equal intervals of time. For e.g. a man walking in a park.
Graph of Non-uniform motion
Time
(hr) Distance (km)
1 10
2 15
3 17
4 30
5 45
6 80
7 90

1, 40
2, 80
3, 120
4, 160
5, 200
6, 240
7, 280
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7 8
Distance (km)
TIme (hr)
Distance vs Time

Graph 2 – Non-uniform motion
Speed and Velocity
Speed – Distance covered per unit time is called speed
Average speed = Total distance covered
Total time taken

v = s
t
where v = speed
s = distance travelled
t = time taken

Velocity – Speed with direction is called velocity
Displacement per unit time is called velocity
Direction of velocity is same as the direction of displacement or motion.

v = displacement
time taken

Average velocity = initial velocity + final velocity
2
vav = µ + v
2

where µ = initial velocity
v = final velocity

1, 10
2, 15
3, 17
4, 30
5, 45
6, 80
7, 90
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8
Distace (km)
Time (hr)
Distance vs time
Page 4

Chapter 8 Motion
Motion – An object that changes its position with respect to time is known to be in motion.
Rest – An object is said to be at rest when it does not change its position with respect to time.
A reference point is required to describe a motion.
For e.g.
1. A car is moving at 60km/hr. It means that the car is moving with respect to its surrounding. The
reference point here is the surrounding.
2. A person travelling by a bus. The bus and the person are in motion with respect to the surrounding i.e.
the plants, trees road etc. The reference points here are the surroundings.
But the person and the bus are at rest with each other because they are moving at same speed and the
man always remain at one point inside the bus. The reference point in this case is the bus for the man
and vice-a-versa.

Motion is a straight line
Describing the motion in a straight line –
The point from where an object stars moving is treated as its reference point.
Distance – the total path length covered by the object from its reference point. Distance only has magnitude
(magnitude = numerical value)
Displacement – The shortest distance covered by an object from its reference point. Displacement has both
magnitude and direction.
The shortest distance is always a straight line dram from the reference point to the point of end
of the motion.

E.g.
O    A    B     C

0              20    40    60 km

Consider an object moves from point O to C and then comes back to point A
Distance covered by the object will be = OC + CA
= 60 + 40
= 100 km
And
Displacement = Shortest distance from the reference point i.e. point O to the end point of end of motion i.e.
point A, which is OA
Hence, displacement = OA = 20km to the right or west of the reference point
Magnitude  Direction
Uniform motion – An object is said to be in uniform motion when it covers equal distances in equal interval of
times. For e.g. A car covered 40km in each hour.
Graph for Uniform motion
Time  (hr) Distance (km)
1 40
2 80
3 120
4 160
5 200
6 240
7 280

Graph 1 – Uniform motion
Non – uniform motion – An object is said to be in non-uniform motion when it covers unequal distance in
equal intervals of time. For e.g. a man walking in a park.
Graph of Non-uniform motion
Time
(hr) Distance (km)
1 10
2 15
3 17
4 30
5 45
6 80
7 90

1, 40
2, 80
3, 120
4, 160
5, 200
6, 240
7, 280
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7 8
Distance (km)
TIme (hr)
Distance vs Time

Graph 2 – Non-uniform motion
Speed and Velocity
Speed – Distance covered per unit time is called speed
Average speed = Total distance covered
Total time taken

v = s
t
where v = speed
s = distance travelled
t = time taken

Velocity – Speed with direction is called velocity
Displacement per unit time is called velocity
Direction of velocity is same as the direction of displacement or motion.

v = displacement
time taken

Average velocity = initial velocity + final velocity
2
vav = µ + v
2

where µ = initial velocity
v = final velocity

1, 10
2, 15
3, 17
4, 30
5, 45
6, 80
7, 90
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8
Distace (km)
Time (hr)
Distance vs time
Time  (hr) Distance (km)
1 40
2 80
3 120
4 160
5 200
6 240
7 280

Graph 3 - Distance vs Time at constant velocity

Acceleration – The rate of change of velocity is known as acceleration

Acceleration = Change in velocity
Time taken

a = v - µ
t
v = final velocity
µ = initial velocity
t = time taken

Graph
Time  (min) Velocity (km/hr)
1 10
2 20
3 30
4 40
5 50
6 60
7 70

1, 40
2, 80
3, 120
4, 160
5, 200
6, 240
7, 280
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7 8
Distance (km)
Time (hr)
Distance vs Time
Page 5

Chapter 8 Motion
Motion – An object that changes its position with respect to time is known to be in motion.
Rest – An object is said to be at rest when it does not change its position with respect to time.
A reference point is required to describe a motion.
For e.g.
1. A car is moving at 60km/hr. It means that the car is moving with respect to its surrounding. The
reference point here is the surrounding.
2. A person travelling by a bus. The bus and the person are in motion with respect to the surrounding i.e.
the plants, trees road etc. The reference points here are the surroundings.
But the person and the bus are at rest with each other because they are moving at same speed and the
man always remain at one point inside the bus. The reference point in this case is the bus for the man
and vice-a-versa.

Motion is a straight line
Describing the motion in a straight line –
The point from where an object stars moving is treated as its reference point.
Distance – the total path length covered by the object from its reference point. Distance only has magnitude
(magnitude = numerical value)
Displacement – The shortest distance covered by an object from its reference point. Displacement has both
magnitude and direction.
The shortest distance is always a straight line dram from the reference point to the point of end
of the motion.

E.g.
O    A    B     C

0              20    40    60 km

Consider an object moves from point O to C and then comes back to point A
Distance covered by the object will be = OC + CA
= 60 + 40
= 100 km
And
Displacement = Shortest distance from the reference point i.e. point O to the end point of end of motion i.e.
point A, which is OA
Hence, displacement = OA = 20km to the right or west of the reference point
Magnitude  Direction
Uniform motion – An object is said to be in uniform motion when it covers equal distances in equal interval of
times. For e.g. A car covered 40km in each hour.
Graph for Uniform motion
Time  (hr) Distance (km)
1 40
2 80
3 120
4 160
5 200
6 240
7 280

Graph 1 – Uniform motion
Non – uniform motion – An object is said to be in non-uniform motion when it covers unequal distance in
equal intervals of time. For e.g. a man walking in a park.
Graph of Non-uniform motion
Time
(hr) Distance (km)
1 10
2 15
3 17
4 30
5 45
6 80
7 90

1, 40
2, 80
3, 120
4, 160
5, 200
6, 240
7, 280
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7 8
Distance (km)
TIme (hr)
Distance vs Time

Graph 2 – Non-uniform motion
Speed and Velocity
Speed – Distance covered per unit time is called speed
Average speed = Total distance covered
Total time taken

v = s
t
where v = speed
s = distance travelled
t = time taken

Velocity – Speed with direction is called velocity
Displacement per unit time is called velocity
Direction of velocity is same as the direction of displacement or motion.

v = displacement
time taken

Average velocity = initial velocity + final velocity
2
vav = µ + v
2

where µ = initial velocity
v = final velocity

1, 10
2, 15
3, 17
4, 30
5, 45
6, 80
7, 90
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8
Distace (km)
Time (hr)
Distance vs time
Time  (hr) Distance (km)
1 40
2 80
3 120
4 160
5 200
6 240
7 280

Graph 3 - Distance vs Time at constant velocity

Acceleration – The rate of change of velocity is known as acceleration

Acceleration = Change in velocity
Time taken

a = v - µ
t
v = final velocity
µ = initial velocity
t = time taken

Graph
Time  (min) Velocity (km/hr)
1 10
2 20
3 30
4 40
5 50
6 60
7 70

1, 40
2, 80
3, 120
4, 160
5, 200
6, 240
7, 280
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7 8
Distance (km)
Time (hr)
Distance vs Time

Graph 4 - Velocity vs Time at uniform acceleration

The area under two points in a velocity time graph gives distance covered in that time
The distance between time interval D (3hr) and C (5hr) is given by the area of the trapezium ABCD

Area of trapezium = ½(b 1 + b2)*h
Area of trapezium = ½(AD + BC)*h

= ½*(30+50)*2   (height = 5 – 3 (time period))
= ½(80)*2
= 80km

But if the object moves with constant velocity and there is no acceleration
Same velocity at all time

Velocity vs time graph at zero acceleration

1, 40 2, 40 3, 40 4, 40 5, 40 6, 40
0
5
10
15
20
25
30
35
40
45
0 1 2 3 4 5 6 7
Velocity (km/hr)
Time (hr)
Velocity vs time
1, 10
2, 20
3, 30
4, 40
5, 50
6, 60
7, 70
0
10
20
30
40
50
60
70
80
0 1 2 3 4 5 6 7 8
Velocity km/hr
TIme (min)
Velocity vs time
A
B
C
D
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