L. R. & S. M. VISSANJI ACADEMY
SECONDARY SECTION - 2016-17
PHYSICS - GRADE: IX
MOTION IN ONE DIMENSION
Important points to remember:
 An object is said to be at rest if it does not change its position with respect to its immediate surroundings.
 An object is said to be in motion if it changes its position with respect to its immediate surroundings.
 The state of rest or motion is purely relative and it is the observer and the surrounding that decide whether a given object is to
be regarded at rest or in motion. Hence, all motion is relative, there is no absolute rest.
 To study the motion of an object, one has to study the change in the position of the object with respect to its surroundings
 One dimensional motion: When a body moves along a straight line path, its motion is said to be the one dimensional motion. For
eg. motion of a train along a railway track, a fruit falling freely under gravity.
 Scalar quantities: Scalar quantities are those physical quantities which are expressed only by their magnitude. To express a
scalar quantity completely, we need to know the numerical value i.e. magnitude and the unit in which the quantity is being
measured.
 Vector quantities: Vector quantities are those quantities which require the magnitude as well as direction in order to be
described completely. To express a vector quantity completely, we need to know the numerical value i.e. magnitude, the unit in
which the quantity is being measured and the direction as well.
Distance
Displacement
• The length of the path cevered by the bvody is
called the distance travelled by the body.
• The shortest distance travelled by the body
from its initial position to the final opsition in a
specified direction is called dispacement.
• It is a vector quantity
• Dispalcement does not depend upon the path
followed by body. It depends only on the final
and initial position of the object.
• It can be positive or negative depending on its
direction.
• Its magnitude can be less than or equal to the
distance, but it can never be greater than the
distance.
• It is zero if the distance is zero but it can be
zero even if the distance is not zero.
• It is a scalar quantity.
• Distance depends upon the path followed by
the object.
• It is always positive.
• It can be more than or equal to the magnitude
od displacement.
• It can never be zero for a moving body
SPEED: Speed of the body is the rate of change of distance with time. It is a scalar
quantity.
VELOCITY: The velocity of the body is the distance travelled per second by the body
The S.I. unit of speed is metr per second and its C.G.S unit is cm per second.
in a specified direction.The rate of change of dispacement of a body with time is called
velocity. It is a vector quantity.
The speed is always positive since the direction is not taken into consideration.
The unit of velocity speed is metr per second and its C.G.S unit is cm per second.
The velocity can be positive or negative depending upon the direction of motion.
Uniform speed: Non-uniform
A body is said speed: A body
is said to be
to be moving
moving with
with uniform
non-uniform
speed if it
covers equal
speed if it
distances in
covers unequal
distances in
equal intervals
of time
equal intervals
Instantaneous
Average
speed: It is
speed: the
the speed of
total distance
the object at a
travelled by
specific instant
the body to
or at a
the total time
particular point
of the journey
of the path
Uniform velocity:
If a body travels
equal distances
in a particular
direction in equal
intervals of time,
the body is said
to be moving
with uniform
velocity
Non-uniform
velocity:
If the body moves
unequal distances
in a partiucular
direction in equal
intervals of time,
but its direction of
motion does not
remain the same,
then the velociyt of
the body is said to
be non-unform
Instantaneous
velocity:
for a body
moving with
variable velocity,
the velocity of
the body at any
instant is called
its instantaneous
velocity.
Average velocity:
If the velocty of
abodymoving in a
particular direction
changes with time,
the ratio of
displacement to
the time taken in
entire journey is
called its
average velocity
ACCELERATION:


The rate of change of velocity with time is called acceleration. It is a vector quantity. Its direction is the direction in which its velocity
changes. S.I. unit is m/s2 or ms-2
The acceleration can be positive or negative. Negative acceleration is called as retardation or deceleration. The positive sign of acceleration
shows that the velocity of the body is increasing with time while the negative sign shows that the velocity of the body is decreasing with
time.

Uniform acceleration: An object is said to be moving with uniform acceleration if its velocity changes by equal amounts in equal intervals of
time.

Non-uniform acceleration: An object is said to be moving with non-uniform or variable acceleration if its velocity changes by unequal
amounts in equal intervals of time.

Acceleration due to gravity: when a body falls freely under gravity, the acceleration produced in the body due to earth’s gravitational
attraction is called the acceleration due to gravity (g). If a body falls down, its velocity increases with time. So the acceleration is +g, while if
the body moves vertically upwards, its velocity decreases with time. So the acceleration is –g ( or the retardation is g)
GRAPHICAL REPRESENTATION OF LINEAR MOTION
Displacement-time graph: In the displacement-time (s-t) graph, the time is taken on x-axis and the displacement on y-axis.
Properties of (s-t) graph:
 It gives the distance or dis[placement of the body at any instant.
 As sped/velocity id s/t, the slope of the (s-t) graph gives the speed or velocity of the body.
 If (s-t) graph is a straight line, then speed/velocity of body is uniform
 If (s-t) graph is not a straight line, then the speed/velocity of the object is non-uniform.
 (s-t) graph is parallel to time axis, then the body is in rest position.
 (s-t) graph can never be parallel to y-axis.
 If (s-t) graph is curved, tangent at any instant of the curve gives the speed of velocity of the object.
Velocity-time graph: In velocity-time (v-t) graph, time is taken on x-axis and velocity is taken on the y-axis with proper time.
Properties of (v-t) graph:
 It gives the speed or velocity of the object at any instant.
 The slope of the (v-t) graph gives the acceleration of the object.
 If the (v-t) graph is a straight line, then the acceleration of the object is uniform.
 If the (v-t) graph is a not a straight line, then the acceleration of the object is non-uniform.
 The (v-t) graph can never be parallel to the y-axis.
 The area enclosed between the (v-t) sketch and x-axis gives the distance/ displacement of the object.
Acceleration-time graph: In acceleration-time (a-t) graph, time is taken on x-axis and acceleration is taken on the y-axis.
Properties of (a-t) graph:
 It gives the acceleration of the object at any instant.
 The area enclosed between the (a-t) sketch and x-axis gives the speed/velocity of the moving object.
 If the object is at rest, then the (a-t) graph will be along x-axis.
 If the graph is not a straight line or curved, then the acceleration or retardation is non-uniform.
EQUATION OF MOTION: Consider a body is moving in a straight line with uniform acceleration (a) having initial velocity (u). after time (t), its
velocity becomes (v). During this time (t), it travels the distance (S). Then the equations of motion are as follows:
First equation of motion: v = u + at
1
Second equation of motion: S = ut + 2 at2
Third equation of motion: v2 = u2 + 2aS