This content explains the concept of uniform circular motion, defining it as movement in a circle at a constant speed, and explores its key characteristics including velocity, acceleration, and the necessary centripetal force.
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hi friends i'm sure you played with the
ball and rope
what type of motion is this ball in
or if you look up at the fan and let's
say there's a sticker on the fan blade
what motion is the sticker in or the
earth moving around the sun
that's right these are all examples of uniform
uniform
circular motion and that's going to be
the topic of this video
i'm sure by the end of the video the
concepts are going to be
super clear to you to understand the
term uniform circular motion
let's break it down there are three
words here
uniform circular and motion
let's start from the back motion means
a body needs to be moving circular means
the path of the moving body has the
shape of a
circle and uniform means the body is
moving at a
constant speed so body moving in a circle
circle
at a constant speed is known as uniform
circular motion now let's apply this
definition of
uniform circular motion to our ball example
example
so as you can see the ball is moving
and it's moving in a circle
the ball is moving at a constant speed
which means it's moving at the same pace
it's not going
faster or slower of course it's hard for me
me
to keep it at a constant speed and
that's why the
fan is a better example of uniform
circular motion
so when you switch on the fan and give
the fan
some time to reach its fixed speed
now if you consider this sticker on the
fan blade
can you see it's in uniform circular motion
motion
it's moving in a circle at a fixed speed
how do we calculate the speed in uniform
circular motion
we know that speed is distance by time
let's say the body takes t seconds to complete
complete
one full revolution so that's t
seconds to complete one full circle
now what is the distance traveled here
that's right
it's the circumference of the circle
so that's 2 pi r where r
is the radius of the circle so the speed
of the body is
2 pi r by t or we say that the magnitude
of the velocity
is 2 pi r by t let's place the concept
of uniform circular motion
and the formula to calculate its velocity
velocity
on our concept board we know that the
body in uniform circular motion
is moving at a constant speed
now an interesting question is is the
body also moving at a
constant velocity what do you think
that's right the velocity is not constant
constant
remember velocity is speed with direction
direction
so the speed here is constant but is the
direction also constant
why don't you try walking around the
can you feel that your direction is
changing all the time
so if the direction is changing velocity
is also changing
so in uniform circular motion velocity is
is
not constant let's consider the
ball and rope example now what is the
direction of the velocity of the ball at
any instant to visualize
you can imagine that we cut the rope or
if i leave the rope
in which direction will the ball go
so let's go ahead and try it out
i'm going to leave the rope and you
carefully look
which direction the ball is going to go
are you ready
one two three
now let's take a look at the slow motion replay
replay
in the slow motion replay can you see
that the ball goes off
in a straight line when i leave the rope
if you draw the radius of the circle at
that point
the direction of the velocity is
perpendicular to the radius of the circle
circle
this is called a tangent to the circle
at that point
that's why it's called a tangential velocity
velocity
similarly if i set the ball into uniform
circular motion again
and now i leave it at a different place
if we look at the slow motion replay can
you see that the ball
flies off in a straight line that is a
tangent to the circle
at that point now we know that a body in
uniform circular motion
is moving in a circle at a constant speed
speed
but changing velocity because the
direction is changing
an interesting question is is there any
acceleration here
the answer is yes it's an accelerated motion
motion
now if you look only at the speed the
speed is constant
so it looks like there's no acceleration
but remember acceleration is the rate of
change of
velocity the magnitude of velocity may
be same
but the direction is definitely changing
as we saw
so this is clearly an accelerated motion
we know that the direction of the
velocity is along a
tangent to the circle but what is the
direction of the
acceleration now that's a little more tricky
tricky
so to simplify first we look at the force
force
and then we'll come back to the
direction of acceleration
since in uniform circular motion there
is an acceleration
there must be some force involved
let's look at the force in uniform
circular motion
so try swinging the ball around like this
this
or maybe for the force i think it might
be easier to visualize
if you swing the ball around like this
so where is the force here that's right
it's in the rope it's the tension in the
rope here
now what is the direction of the force
that's right it's inwards towards the
center of the circle which is my hand here
here
so my hand is continuously pulling the
ball with the rope
towards the center and the direction of
the force
is continuously towards the center of
the circle
this is known as centripetal force
because the word centripetal means
center seeking similarly
if you consider the sun and earth example
example
the sun's gravitational force is keeping
the earth
in uniform circular motion the
gravitational force
is a centripetal force that is it's a
center-seeking force
it's continuously pulling the earth
towards the center of the orbit
which is the sun in this case
now for example let's say today is
sunday and the sun says i'm tired i need
a break
so there's no force on the earth what do
you think is going to happen
that's right the earth is going to fly
off into space
just like the ball when i left the rope
so thankfully the sun never takes a
holiday because
this centripetal force is necessary to
keep a body
in uniform circular motion
we know that the direction of the force
is towards the center
it's a centripetal force now the
direction of the acceleration is
easy because acceleration has the same direction
direction
as the force so the direction of the acceleration
acceleration
is also towards the center of the circle
so this is called a centripetal acceleration
acceleration
and the direction of the acceleration is
always perpendicular
to the direction of the velocity at that instant
instant
as shown here and the acceleration
is only changing the direction of the velocity
velocity
not the magnitude of the velocity
let's put the concepts of velocity acceleration
acceleration
and centripetal force for uniform
circular motion
on our concept board i hope the concept
of uniform circular motion
is crystal clear to you now as we discussed
discussed
the earth going around the sun is an
example of
uniform circular motion but is this
really true your textbooks may also say that
that
but the correct answer is no
because strictly speaking the earth is
not in a uniform
circular motion now why is that
because as you may know the earth's
orbit is not perfectly circular
it's elliptical in shape and you know
that the earth when it's closer to the sun
sun
is moving much faster than when it's
away from the sun
so the earth is not moving at a constant speed
speed
but usually we ignore all these details
and we consider
earth moving around the sun as an
example of
uniform circular motion so this is an
approximation that we make
to watch more science and maths videos
like this
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academy.com
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