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MOTION IN A STRAIGHT LINE
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PHYSICS

MOTION IN A
STRAIGHT LINE

WHAT IS A PARTICLE?
WHAT IS A RIGID BODY?
 A “PARTICLE” is an object which has a negligible dimension.
 RIGID BODY: It is a combination of particles and when an
external force is applied there will be no change in its dimensions.
“PARTICLE”

Are you a PARTICLE
OR
RIGID BODY?
As relative distance is less, you are considered to be a
BODY

As relative distance is large,
person appears as a
PARTICLE & RIGID
BODY
RELATIVE TERMS.
i.e

REST & MOTION
FAN AT REST…..
WHAT IS REST?
TV AT REST…
 If a body does not change its position with respect to surroundings, then
the body is said to be at rest.

WHAT IS MOTION?
MOVING BLADES OF A FAN
MOVING CAR
CHANGES THE POSITION WITH RESPECT TO TIME

ARE THE PASSENGERS IN THE BUS AT REST OR IN MOTION?

 PASSENGERS IN THE BUS ARE AT REST RELATIVE TO
EACH OTHER……

 PASSENGERS IN THE BUS ARE IN MOTION RELATIVE TO
PEOPLE AT BUS STOP

WHAT IS MOTION?
 Motion is change of position with respect to time.
WHAT IS REST?
 A body is said to be at rest when there is no change of position with
respect to time.
 The branch of mechanics that deals with the study of motion of
objects without any reference to the cause of motion is called
kinematics.
 A system of coordinate axis with respect to which an event can be
described is called frame of reference.

REST & MOTION ARE RELATIVE TERMS
 Motion of an object is always with respect to some frame of
reference.
One frame of
reference
Another frame of reference

Let us see how the states of motion and rest are related….
 Rest and motion are relative terms. They are not absolute. A body
can be at rest or in motion with respect to reference frame.
 A man in a moving train is at rest with respect to a co-passenger,
but he is in motion with respect to a man outside the train.
 There is no frame of reference which is perfectly at rest.

1) A particle is an object having negligible ...
a) units
b)
c) magnitude
d) directions
dimensions

2) Rigid body is a combination of particles and when external force is
applied there will be no change in its...
a) magnitude
b)
c) magnitude and direction
d) direction alone
dimensions

3) Rest and motion are ___ terms.
a) absolute
b)
c) relative
d) both (b) and (c)
not absolute

 CRAWLING ANTS
WHAT TYPE OF
MOTION IS THIS?
THIS IS MOTION IN A
STRAIGHT LINE.

 COCKROACH MOVING ON A FLOOR
WHAT TYPE OF
MOTION IS IT?
THIS IS MOTION IN
A PLANE.

 FLYING HONEY BEE
WHAT TYPE OF
MOTION IS IT?
THIS IS MOTION
IN A SPACE.

Motion in one dimension
 Motion in a straight line
Motion in two dimensions
Motion in three dimensions
 Motion in a plane..
 Motion in a space…..
TYPES OF MOTION

1. How many types of motions are there?
a) Two
b)
c) Three
d) One
Four

2. Motion in one dimension is also called ...
a) motion in space
b)
c) motion in a straight line
d) motion under gravity
motion in a plane

Recti
Straight
 Motion along a straight line is called
Rectilinear motion
Ex: The motion of a car on a road.
Linear
Line
+
+

Rectilinear motion need not
be one dimensional
necessarily.
Rectilinear motion can
be any straight line in
any direction
But, it is always
possible that rectilinear
motion be treated as one
dimensional motion

1
2
3
4
-4
-3
-2
-1
1 2 3 4
-4 -3 -2 -1
 Rotation of coordinate system does not
change the rectilinear motion of the car.
x
y
rectilinear motion

SCALAR QUANTITY
 Quantity with magnitude alone and no direction
 Example: Path length, speed
VECTOR QUANTITY
 Quantity with both magnitude and direction follows laws of vector
addition.
 Example: Displacement, velocity.

PATH LENGTH AND DISPLACEMENT
Path length: Total distance travelled by an object from initial to final
position.
HOME COLLEGE
Displacement: Shortest distance between initial and final position.
Path length=DHC+DCM
Displacement=DHM

PATH LENGTH = DISPLACEMENT
Initial position Final position
Path length = DHM
Displacement = DHM
 Path length = displacement

Path length=DHM+DMH
Displacement=0
Path length≠0
But displacement=0

 The magnitude of displacement may or may not be equal to the path
length travelled by an object.
 The magnitude of the displacement for a complete motion may be
zero but the corresponding path length is not zero.

1. Correct statement among the following is...
1) When displacement is zero, distance travelled is not zero.
2) When displacement is zero, distance travelled is also zero.
3) When distance is zero, displacement is not zero.
4) Distance travelled and displacement are always equal.

2. The numerical ratio of displacement to distance is...
1) always less than 1
3) always equal to 1
4) may be less than 1 or equal to 1
2) always greater than 1

3. The total distance travelled by an object from initial to final position is
known as ...
a) speed
b)
c) displacement
d) distance
path length

If an object is moving along a straight line covers equal distance at
equal intervals of time, however small the time interval may be, it is said
to be in uniform motion along a straight line.
What is uniform motion?

SPEED: Rate at which an object covers distance
 Scalar quantity
Speed =
Path length
Time taken
VELOCITY: Rate at which an object changes its position in a given
direction.
 Vector quantity
Velocity =
Displacement
Time taken

Example: Speed and velocity
During total journey
Let DHM = 2km, Time (T) = 1 hr
Path length=DHM+DMH
Displacement = 0
= 2+2 = 4 km

Speed =
Path length
Time taken
=
4
1
Velocity =
Displacement
Time taken
=
0
1
= 4 km/hr
= 0

1. Speed is a ___quantity.
a) scalar
b)
c) neither scalar nor vector
d) both scalar and vector
vector

2. Velocity is a ___ quantity
a) scalar
b)
c) neither scalar nor vector
d) both scalar and vector
vector

Thank you…

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