hi friends i'm sure you played with the ball and rope like this 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 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 at a constant speed is known as uniform circular motion now let's apply this definition of uniform circular motion to our ball 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 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 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 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 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 remember velocity is speed with direction so the speed here is constant but is the direction also constant why don't you try walking around the room in a circle like this 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 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 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 this is called a tangent to the circle at that point that's why it's called a tangential 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 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 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 so to simplify first we look at the 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 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 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 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 as the force so the direction of the acceleration is also towards the center of the circle so this is called a centripetal acceleration and the direction of the acceleration is always perpendicular to the direction of the velocity at that instant as shown here and the acceleration is only changing the direction of the velocity not the magnitude of the velocity let's put the concepts of velocity 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 the earth going around the sun is an example of uniform circular motion but is this really true your textbooks may also say 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 is moving much faster than when it's away from the sun so the earth is not moving at a constant 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 do check out my website manoj academy.com links are given below the video and if you liked watching this video do give it a thumbs up and share out this video and don't forget to subscribe to my youtube channel and follow my facebook page thanks for watching to try these features and learn more about the course just go to my website manoj academy.com to make it easy i'll put the links below hope you like it and happy learning