Motion Class 9 Notes CBSE Science Chapter 8
CBSE NCERT Class 9th Revision Notes Science contains Revision Notes of Ch 8 Motion topics given in textbook are part of Revision Notes for Class
This Chapter Notes includes topic/concepts wise explanations for all the topics provided in the book such as distance, displacement, speed, velocity, linear, rotary, Oscillatory motion, rotational motion, Translational motion, uniform motion, Non- uniform motion, periodic motion, Circular motion, Linear motion, reciprocating, oscillating, time and distance.
Well prepared Class 9th Science all Chapters Notes will guidance students understand the topics ,concepts and themes covered in all the chapters of Ncert Text book of 9th
Motion CBSE Class 9 Notes
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What is motion?
If the location of an object changes with time the object is said to be in motion.
Introduction
➢ A Reference Point is used to describe the location of an object. An object can be referred through
many reference points.
➢ Origin – The reference point that is used to describe the location of an object is called Origin.
➢ For Example, a new restaurant is opening shortly at a distance of 5 km north from my house. Here,
the house is the reference point that is used for describing where the restaurant is located.
Types of Motion
There are three types of motion:
➢ Translatory motion
➢ Rotatory motion
➢ Vibratory motion
Translatory motion
➢ A particle in translator motion moves from one point in space to another. This movement may be
in a straight line or in a curved path.
➢ Rectilinear motion is defined as motion along
a straight line.
➢ Curvilinear motion is defined as movement
along a curved path.
➢ As an example, consider a car driving down a
straight road.
Rotatory motion
➢ The point of the body describe concentric circles around the axis of motion in rotatory motion.
Vibrational motion
➢ Particles in vibratory motion move back and forth around a fixed point.
Motion in a Straight Line
Distance
➢ The distance covered by an object is described as the total path length
covered by an object between two endpoints.
➢ Distance is a numerical quantity. We do not mention the direction in which an object is travelling
while mentioning about the distance covered by that object.
➢ According to the figure 1 given above, if an object moves from point O to point A then total
distance travelled by the object is given as 60 km.
(Fig. 1)
➢ Displacement – The shortest possible distance between the initial and final position of an object
is called Displacement.
(Fig. 2)
➢ Consider the figure 1 given above, here the shortest distance between O and A is 60 km only.
Hence, displacement is 60 km.
➢ Displacement depends upon the direction in which the object is travelling.
➢ Displacement is denoted by Δx.
= − x x x f 0
Where,
= Final Position on the object
x0
= initial position of the object
➢ Zero Displacement – When the first and last positions of an object are same, the displacement is
zero.
➢ For Example, consider the diagrams given below.
➢ Displacement at point A = 0 because the shortest
distance from A to A is zero.
➢ Negative Displacement and Positive Displacement
➢ Here, displacement of object B is negative
ΔB = Bf – B0 = 7 – 12 = – 5
A negative sign indicates opposite direction here.
Also, displacement of object A is positive
ΔA = Af – A0 = 7 – 0 = 7
What are Scalar and Vector Quantities?
➢ A scalar quantity describes a magnitude or a numerical value.
➢ A vector quantity describes the magnitude as well as the direction.
➢ Hence, distance is a scalar quantity while displacement is a vector quantity.
How is distance different from displacement?
Distance
Distance provides the complete details of the
path taken by the object
Displacement does not provide the complete details
of the path taken by the object
Distance is always positive
Displacement can be positive, negative or zero
Displacement
It is a scalar quantity
It is a vector quantity
The distance between two points may not be
unique
Displacement between two points is always unique
What is uniform Motion?
➢ When an object travels equal distances in equal intervals of time the object is said to have a uniform
motion.
➢ E.g. The distance covered by Car A with respect to time is given below:
Car A
Time is seconds
0
5
10
15
20
25
30
35
Distance covered in meters
0
10
20
30
40
50
60
70
What is non-uniform motion?
➢ When an object travels unequal distances in equal intervals of time the object is said to have a nonuniform motion.
➢ E.g. The distance covered by Car B with respect to time is given below:
Car B
Time is seconds
0
5
10
15
20
25
30
35
Distance covered in meters
0
10
15
20
30
60
65
75
➢ The car A travels equal distances in equal time intervals, whereas the car B does not travel equal
distances in equal time intervals.
➢ That is, car A’s motion is an example of uniform motion, whereas car B’s motion is an example
of non-uniform motion.
➢ A body is said to describe uniform motion when it covers distances in equal intervals of time
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