Chapter 8 Motion Class 9 Notes | EduRev

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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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