 Okay, so here you are standing in this train moving at 30 km per second to the right. You jump upwards, what happens? To make things easier, we'll draw some X and Y axes, okay? So just before the jump, what is your velocity in each of these directions? Pause the video now and see if you can have a guess, okay? So I'm standing in this train and the train is moving at 30 km per second. And since I'm staying in the same place relative to the train, I'm also moving to the right, at 30 km per second. I'm moving with the train. And so my overall velocity is represented by this arrow here, okay? What about just after the jump? So let's suppose my leg muscles are such that right after the jump, I'm moving upwards at 10 meters per second, okay? But what's my velocity in the X direction? Pause the video and see if you can guess. So just before the jump, I was moving with a velocity of 30 km per second in the X direction. And just after the jump, I still have that velocity. I'm still moving at 30 km per second. Because for that velocity to change, I'd need some kind of horizontal force to act on me, to slow me down. But that doesn't happen. I just jump upwards. So all that happens is I have a velocity of 10 meters per second added to my velocity of 30 km per second. So overall, my velocity is now diagonal. It has a 30 km per second component and a 10 m per second component. And so because of that, if this is the train and this is you, you will move with the train during the jump. And so from your point of view, you will land exactly where on the train you started.