0:02 hi friends i'm sure you played with the
0:03 ball and rope
0:10 what type of motion is this ball in
0:12 or if you look up at the fan and let's
0:15 say there's a sticker on the fan blade
0:18 what motion is the sticker in or the
0:21 earth moving around the sun
0:24 that's right these are all examples of uniform
0:24 uniform
0:27 circular motion and that's going to be
0:29 the topic of this video
0:31 i'm sure by the end of the video the
0:32 concepts are going to be
0:35 super clear to you to understand the
0:37 term uniform circular motion
0:39 let's break it down there are three
0:41 words here
0:44 uniform circular and motion
0:47 let's start from the back motion means
0:51 a body needs to be moving circular means
0:53 the path of the moving body has the
0:54 shape of a
0:58 circle and uniform means the body is
0:59 moving at a
1:02 constant speed so body moving in a circle
1:03 circle
1:06 at a constant speed is known as uniform
1:09 circular motion now let's apply this
1:10 definition of
1:12 uniform circular motion to our ball example
1:14 example
1:18 so as you can see the ball is moving
1:21 and it's moving in a circle
1:24 the ball is moving at a constant speed
1:26 which means it's moving at the same pace
1:27 it's not going
1:31 faster or slower of course it's hard for me
1:32 me
1:34 to keep it at a constant speed and
1:35 that's why the
1:38 fan is a better example of uniform
1:39 circular motion
1:41 so when you switch on the fan and give
1:42 the fan
1:46 some time to reach its fixed speed
1:48 now if you consider this sticker on the
1:50 fan blade
1:52 can you see it's in uniform circular motion
1:53 motion
1:57 it's moving in a circle at a fixed speed
1:59 how do we calculate the speed in uniform
2:01 circular motion
2:05 we know that speed is distance by time
2:07 let's say the body takes t seconds to complete
2:08 complete
2:11 one full revolution so that's t
2:15 seconds to complete one full circle
2:18 now what is the distance traveled here
2:19 that's right
2:22 it's the circumference of the circle
2:25 so that's 2 pi r where r
2:29 is the radius of the circle so the speed
2:30 of the body is
2:34 2 pi r by t or we say that the magnitude
2:36 of the velocity
2:40 is 2 pi r by t let's place the concept
2:42 of uniform circular motion
2:44 and the formula to calculate its velocity
2:45 velocity
2:48 on our concept board we know that the
2:50 body in uniform circular motion
2:54 is moving at a constant speed
2:56 now an interesting question is is the
2:57 body also moving at a
3:02 constant velocity what do you think
3:04 that's right the velocity is not constant
3:06 constant
3:09 remember velocity is speed with direction
3:11 direction
3:14 so the speed here is constant but is the
3:17 direction also constant
3:19 why don't you try walking around the
3:27 can you feel that your direction is
3:29 changing all the time
3:32 so if the direction is changing velocity
3:33 is also changing
3:36 so in uniform circular motion velocity is
3:37 is
3:40 not constant let's consider the
3:43 ball and rope example now what is the
3:46 direction of the velocity of the ball at
3:49 any instant to visualize
3:52 you can imagine that we cut the rope or
3:53 if i leave the rope
3:57 in which direction will the ball go
4:00 so let's go ahead and try it out
4:02 i'm going to leave the rope and you
4:03 carefully look
4:06 which direction the ball is going to go
4:07 are you ready
4:11 one two three
4:14 now let's take a look at the slow motion replay
4:15 replay
4:18 in the slow motion replay can you see
4:19 that the ball goes off
4:22 in a straight line when i leave the rope
4:24 if you draw the radius of the circle at
4:25 that point
4:28 the direction of the velocity is
4:30 perpendicular to the radius of the circle
4:31 circle
4:34 this is called a tangent to the circle
4:36 at that point
4:38 that's why it's called a tangential velocity
4:40 velocity
4:43 similarly if i set the ball into uniform
4:45 circular motion again
4:49 and now i leave it at a different place
4:51 if we look at the slow motion replay can
4:52 you see that the ball
4:55 flies off in a straight line that is a
4:56 tangent to the circle
5:00 at that point now we know that a body in
5:01 uniform circular motion
5:03 is moving in a circle at a constant speed
5:04 speed
5:07 but changing velocity because the
5:09 direction is changing
5:12 an interesting question is is there any
5:14 acceleration here
5:18 the answer is yes it's an accelerated motion
5:19 motion
5:21 now if you look only at the speed the
5:23 speed is constant
5:26 so it looks like there's no acceleration
5:29 but remember acceleration is the rate of
5:30 change of
5:33 velocity the magnitude of velocity may
5:34 be same
5:37 but the direction is definitely changing
5:39 as we saw
5:43 so this is clearly an accelerated motion
5:44 we know that the direction of the
5:46 velocity is along a
5:49 tangent to the circle but what is the
5:50 direction of the
5:53 acceleration now that's a little more tricky
5:54 tricky
5:56 so to simplify first we look at the force
5:57 force
5:59 and then we'll come back to the
6:01 direction of acceleration
6:04 since in uniform circular motion there
6:05 is an acceleration
6:09 there must be some force involved
6:11 let's look at the force in uniform
6:12 circular motion
6:14 so try swinging the ball around like this
6:16 this
6:17 or maybe for the force i think it might
6:19 be easier to visualize
6:23 if you swing the ball around like this
6:26 so where is the force here that's right
6:29 it's in the rope it's the tension in the
6:31 rope here
6:34 now what is the direction of the force
6:37 that's right it's inwards towards the
6:40 center of the circle which is my hand here
6:42 here
6:44 so my hand is continuously pulling the
6:45 ball with the rope
6:48 towards the center and the direction of
6:49 the force
6:51 is continuously towards the center of
6:53 the circle
6:56 this is known as centripetal force
6:58 because the word centripetal means
7:02 center seeking similarly
7:03 if you consider the sun and earth example
7:05 example
7:07 the sun's gravitational force is keeping
7:08 the earth
7:11 in uniform circular motion the
7:12 gravitational force
7:15 is a centripetal force that is it's a
7:17 center-seeking force
7:19 it's continuously pulling the earth
7:21 towards the center of the orbit
7:25 which is the sun in this case
7:26 now for example let's say today is
7:29 sunday and the sun says i'm tired i need
7:30 a break
7:34 so there's no force on the earth what do
7:36 you think is going to happen
7:38 that's right the earth is going to fly
7:39 off into space
7:42 just like the ball when i left the rope
7:44 so thankfully the sun never takes a
7:46 holiday because
7:49 this centripetal force is necessary to
7:50 keep a body
7:53 in uniform circular motion
7:55 we know that the direction of the force
7:57 is towards the center
8:00 it's a centripetal force now the
8:02 direction of the acceleration is
8:05 easy because acceleration has the same direction
8:06 direction
8:08 as the force so the direction of the acceleration
8:09 acceleration
8:13 is also towards the center of the circle
8:15 so this is called a centripetal acceleration
8:17 acceleration
8:20 and the direction of the acceleration is
8:21 always perpendicular
8:24 to the direction of the velocity at that instant
8:25 instant
8:29 as shown here and the acceleration
8:31 is only changing the direction of the velocity
8:32 velocity
8:35 not the magnitude of the velocity
8:38 let's put the concepts of velocity acceleration
8:39 acceleration
8:42 and centripetal force for uniform
8:43 circular motion
8:47 on our concept board i hope the concept
8:48 of uniform circular motion
8:52 is crystal clear to you now as we discussed
8:52 discussed
8:55 the earth going around the sun is an
8:56 example of
8:59 uniform circular motion but is this
9:02 really true your textbooks may also say that
9:03 that
9:07 but the correct answer is no
9:09 because strictly speaking the earth is
9:10 not in a uniform
9:14 circular motion now why is that
9:16 because as you may know the earth's
9:19 orbit is not perfectly circular
9:21 it's elliptical in shape and you know
9:23 that the earth when it's closer to the sun
9:24 sun
9:26 is moving much faster than when it's
9:28 away from the sun
9:31 so the earth is not moving at a constant speed
9:31 speed
9:34 but usually we ignore all these details
9:35 and we consider
9:37 earth moving around the sun as an
9:38 example of
9:41 uniform circular motion so this is an
9:44 approximation that we make
9:46 to watch more science and maths videos
9:47 like this
9:50 do check out my website manoj academy.com
9:52 academy.com
9:55 links are given below the video and if
9:57 you liked watching this video
9:59 do give it a thumbs up and share out
10:00 this video
10:03 and don't forget to subscribe to my
10:04 youtube channel
10:07 and follow my facebook page thanks for watching
10:08 watching
10:11 to try these features and learn more
10:12 about the course
10:16 just go to my website manoj academy.com
10:20 to make it easy i'll put the links below
