Motion and its types - Motion and Time - CBSE Class 7 Science Video Lecture

good morning children today we shall
talk about motion what is the difference
between the bird sitting on a branch and
a flying bird or a parked car and a
moving car or a train standing on the
platform and a moving train the answer
is very simple in the first case things
are not moving that is they are at rest
and in the second case they are moving
so when an object is moving it is said
to be in motion or we can say when a
body moves from one place to another it
is known as the motion of that body but
if you sit inside a moving train and see
outside you will feel as if not just
people on the platform but even the
trees are moving this is confusing so
how do we know that an object is in
motion or not let us take an example you
are standing at a railway platform and
then a train passes from there you see
the train coming from one end of the
platform and after some time it passes
you and goes away
it means when the object moves its
position changes with respect to another
stationary object with time like when
you first saw the train it came from one
end of the platform that time the
distance between the train and that and
was very small as the Train moved
further the distance from that and
increases or we can say when the Train
moves its position with respect to the
platform changes with time so while
standing on the platform how did you
realize that the train has started
moving the platform where you stood did
not move but the Train changed its
position with time and moved away from
the platform and you knew it was moving
an object is in motion if its position
changes with time in relation to a
stationary object such as a tree or a
house or a platform so when we say an
object is moving it is always with
respect to another object which is not
moving that is it is stationary like
when we say a car is moving it is moving
with respect to stationary trees poles
buildings on the road flying bird moving
car moving fan or rotation of Earth all
are moving or in motion but are all
these motions similar to each other or
do they differ from each other yes there
are different types of motion and not
all types of motion are same when a car
moves on a straight road its motion too
is in a straight line even a stone
falling from a height follows a straight
path like we saw in the circus the
artist doing a balancing act on the
tightrope was also cycling on a
tightrope the motion of the cycle was in
a straight line along the rope so when
the motion of body is in straight line
that is when a body is moving along a
straight line we call it linear or
rectilinear motion now let us see
another type of motion here the Joker is
whirling a stone or a ball tied to a
thread observe the motion of the stone
closely we will find that the stone
moves along a circular path so in this
motion the distance of the stone from
the Joker's hand
remains the same this type of motion is
called circular motion as we saw in the
circus the horse was running along a
circular path assuming it followed the
circular path correctly its motion can
be said to be a circular motion but in
real life the various motions can either
be exactly in a straight line nor in an
exact circular path as we know generally
a car moves in a straight line but the
roads are not always straight also we
need to take different routes for
different destinations so a car can move
along a curved path also the body is
moving along a curve it is said to have
a curvilinear motion a moving car taking
a turn is an example of curvilinear
motion as we saw in the circus the Joker
was riding the bicycle along a curved
path this was an example of curvilinear
motion are there another types of motion
let us see assume that you are replacing
the bearings in a wheel of your bicycle
to test you hold the axle vertically and
give it a spin the axle at the center of
the wheel is stationary while spinning
the wheel is not moving forward instead
the wheel is turning around the axle
every point on the V undergoes a
circular motion about an axis of
rotation such motion around an axis of
rotation is called rotatory motion the
earth spinning around its imaginary axis
is also an example of rotatory motion
let us see a spinning top
if we observe closely not all the parts
of the talk moved the same distance in a
given interval of time the topmost part
moves a smaller distance while the
extended part moves a greater distance
in a given time like we saw in the
circus The Joker was spinning a ball on
his finger this was the example of
rotatory motion some motions repeat
themselves again and again like when you
are swinging in the garden or the earth
moving around the Sun in the case of
Earth the Earth continues to revolve
around the Sun and that too in a fixed
orbit it completes one revolution in a
fixed time and this motion is repeated
similar to the Earth's revolution around
the Sun many objects repeat the motion
after a fixed interval of time this type
of motion is called periodic motion the
to and fro motion of the pendulum of a
clock also repeats itself in a fixed
interval of time so it is also a
periodic motion as we saw in the circus
the trapeze artists were swinging back
and forth that was also an example of
periodic motion the motion of our hands
why we walk and the motion of fingers as
they type on a keyboard or the motion of
fingers as they play a song on the
keyboard these are some of the motions
which repeat but do they repeat in a
regular interval no these motions don't
repeat that regular intervals so any
type of motion that does not repeat
itself after equal interval of time is
called non periodic motion so now we
know quite a lot about different types
of
motions coming back to the circus show
you all must have enjoyed watching the
balancing act on the tightrope now let
us see what type of motion was there
when the artist was cycling on the rope
you will say that is easy to answer as
the cycle was moving along the straight
line its motion was rectilinear motion
and that is correct but wait a minute
how about sweets observe the wheels the
wheels of the cycle is executing
rotatory motion the axis of rotation
being the axle of the wheel so there are
two types of motions going on
simultaneously let us take another
example have you observed closely the
motion of a ball on the ground here the
ball is rolling on the ground it is
rotating as well as moving forward on
the ground thus the ball undergoes a
rectilinear motion as well as rotating
motion now let us see a Earth from the
space what type of motion can you see
now yes the earth is rotating about its
own axis and it is also revolving around
the Sun in an elliptical path at the
same time it has a rotatory as well as
curvy linear motion so many times an
object may have a combination of more
than one type of motion at the same time
as we saw while cycling on the tightrope
there was both rectilinear as well as
rotate three motion so today we have
learnt an object is said to be in motion
if its position with respect to another
stationary object changes with time let
us see what all types of motions we saw
in the circus
the cycling on a tightrope this was a
rectilinear motion the Joker
cycling around the curved part it was a
curvy linear motion same way the horse
running around the fixed circular part
was circular motion the Joker spinning
the ball on his finger
this was rotatory motion the trapeze
artist swinging back and forth
this was periodic motion and lastly an
object may have a combination of more
than one type of motion at the same time
like while cycling on a tightrope the
motion is along the straight line but
the wheels of cycle execute rotatory
motion that was all about the motion and
its type
see you in the next class bye bye kids