And that is another reason, why I have to rewrite them in terms of X Y and in terms of u v. That means, I need to rewrite these by changing this X 0 Y 0 to X and Y and changing

this 2 u dot and v dot. We have to do that, we will be doing it, you know eventually, but we will have do that by using coordinate transformation.
So, this remember that one one more thing, I did not write, I write it down. See, rotation we normally, do not tell this is u, this is v, rotation motion is always known as r. The velocity like u v and you call it r. In far, I should write it down, because it is this thing body access (Refer Slide Time: 50:33), u is always velocity along body x, v is this is what we call sway velocity this what is called sway velocity. Remember sway velocity is always, when I am sitting on the body, how much it is transferring transferring and this one r r is known as yaw velocity.
Actually, you will see from here (Refer Slide Time: 51:12), that r is psi dot. Remember that when you are doing dot. You it is always the rate of change of heading. Remember psi dot psi dot not drift dot. It is not beta beta dot. So, r is actually (No audio from 51:25 to 51:39), but for unfortunately, no fortunately r and psi is not sensitive on the axis system that we have chosen.
Simply because my z axis is downward to the piece of paper for both, but I can tell you that, this is not necessarily true for (Refer Slide Time: 51:58) a general 60 of body. If I were to take a submarine or a rocket or a torpedo or a missile, anybody then I would have actually much more complex equations. Then what I am going to have, because there r also will have change.
In in any case, what we will be doing then next class is that, we are going to their first write the equation of motion. That is very important, but as I kept telling equation of motion is going to tell me something like this.