Projectile Motion:
What is projectile motion? When a particle is projected at certain angle. Suppose this is x and this is y, and we have thrown a ball like this from here, we have thrown it u initial speed at theta angle, so this object will perform this motion. Yes or no? This is called projectile motion. And we are dealing with case 1.
It is called ground to ground projectile. It is called ground to ground projectile because the point of projection and point of landing, both are on the same horizontal level. So that is called ground to ground projection. Can I say that, see this ball has gone up and it has come down. Now add this to this. This vertical motion which we called as free fall in the previous topic, in that if we add this linear motion then what will we see. The combined effect of both and that will be known as the projectile motion. This two dimensional motion is basically the combination of this linear motion and this linear motion. And what is fascinating is that this is the motion which we already know a lot about. Yes or no?
So let’s draw the basic, we will define motion for x and y, okay. Initial velocity x, acceleration x, displacement x. Initial velocity y, acceleration y, displacement y. This is the technique of learning projectile motion by making this table first of all. We will fill in the values in this table, okay.
Now we had learnt about a topic on vectors. And on that topic what had I told you, I had told you that the most useful thing for us will be. Component. u velocity at theta angle. Can you make two components of this velocity? What will be this component, class?
u cos theta. And what will be that component?
[students answering]U sine theta.
Now let’s fill in the table. Whatever you can understand by looking at this information we will fill this table, okay. Tell me ux initial velocity along x axis what will that be? u cos theta. Initial velocity along y axis, what will that be? u sine theta. Acceleration along x, acceleration along x. There is only one acceleration working on this, which one is that g. And where is it working downward. So what is horizontal acceleration, yes or no? So ax zero. That’s critical. What is ay? g or minus g.
[minus g]In 1D what was the technique we had made to decide the sign for displacement and acceleration. According to that rule it will be minus g, yes or no? What is horizontal displacement? You don’t know. This will be the horizontal displacement. Right. So let’s call it R, which we don’t know. What is vertical displacement? What is total vertical displacement?
