 So this is one section of motion in 2D, the other section of motion in 2D is circular motion alright and then comes the projectile motion alright. So first we will study the circular motion because I think most of you will, how many of you are there in the bridge program? Okay how many of you are not there? That will be lesser, only 3-4. Okay so we will be doing projectile motion again. So here lies your chance to again learn it from scratch and those who think that they have already learned the projectile motion properly here is your chance that you have one week where you can do higher level questions on whatever you have done. So since many of you have already done projectile motion before I will be doing projectile motion at the end, right now I am doing the circular motion okay please write down circular motion in a different way when you will say that object is having circular motion speed is constant but velocity keeps on changing but it can be done like this also right, speed can be constant velocity keeps on changing but this is not a circular motion so I can go like this from point A to B I travel like that, is this circular motion? Acceleration is in a project, it comes back speed is, speed should all motion, speed should be constant? No. So how will you say that object will move or should move in a certain way? No, it will move in a certain way. It will move in a certain way. Dispatch must be, as in although that could be, I mean you are describing it but it is not concise, I mean it is not very very clear, crystal clear Anyone, Ajay tell me how you make a circle as in when the circle will be made, when distance from the fixed point is fixed okay, when the distance from a fixed point is fixed which is radius and the particle will say right is circular motion okay, now what I am doing is that you draw these two points A and B are you seeing any circular motion here in the room? Fan is one of the examples that you have taken so suppose this is a fan, entire fan is moving in a circular motion? No, blades are moving in a circular motion as if the entire blade in a same circle and each point, let's say this is the point the radius is this much? I mean from here to here is a circular motion of point two this point three is also moving in a circle like that now you can see that as you move towards the center the radius is decreasing and in the same time one is going to one dash two is going to two dash and three is going to three dash one is tearing the more distance yes or no? so point number one is going faster point number two has to go slower because it has to travel lesser distance in the same time and point number three goes with the least speed but whatever it is, we can see that it is all the points in the fan they are moving in a circular motion center is this axis of rotation only so center of every point on the fan is moving in a circle with the center fixed so we have a concentric circle lot of concentric circles are there we are getting it further studied as in what if you are not at rest suppose you are moving will you see certain direction just like when you are in a train moving pick but I am saying that what you are observing I am not saying actually what it is so you will see that the fan is going in a pick and then fan starts to move let's say rotate now every point with respect to center is moving a circle so the kind of path it will follow is this with respect to you suppose I am going like this fan is at rest and on top of it fan starts to move also so while fan is rotating it is going back like this are you getting it so all the points motion changes with respect to observer who is at rest just as an example it need not be just a fan it could be anything for example if A and B are the two points if I say that distance between A and B is fixed let's say distance between A and B is L and that distance cannot change it cannot increase and it cannot decrease now can point B move how? it is so that the distance between A and B is fixed so when distance between two points is one point it has to move relative to circle only by distance from the fan is increasing the tip of the fan and this point the distance between these two points is fixed and if this point has to move relative to that point it has only one option circle now tell me one more thing now distance between two points is fixed point A and B we have discussed that point B will move in a circle right? can point A move in a circle with respect to B is the center of the fan is always point B observable opposite direction in physics center is just a point where observer is located the center, this point which was center can be moving the circle relative to that point getting it if you observe this B becomes center and A goes in if it is moving the circle because we are at rest and center is also at rest so whatever is happening with respect to center so I am only seeing what can be observed with respect to the center are you able to understand what I am trying to say but if I start to move in a circle like this somehow let's say there is a device which also moves in a circle like this with the fan so will it suppose this point is going like this and there is a point which also travels like this with the same velocity in a circle so this point will come to rest relative to that are you getting it? fine so this point will be at rest now you will observe that point is going in a circle center is moving in a circle okay so when we observe circular motion is observed when circular motion is observed when the distance between the two points when the distance between the two points is fixed when the distance between the two points is fixed and one point is moving relative to other if motion is observed fixed point as in the observer distance from a fixed point if it is constant then this circular motion what I am saying is that the center need not be a fixed point do you understand it is fixed okay point may be in that point fine if we consider that the center is at rest we will observe normal circular motion for here but there is a chapter in New York syllabus it is called rotational motion, rigid body motion you might have heard of it okay it is considered to be the most difficult topic in the entire physics class so circular motion is the beginning of that chapter in fact this should not be the topic of motion in 2D but we are studying it properly now itself so that once that comes you will already have some hangover okay