why does a rocket seem to lose lateral velocity?ty.

[tipsyMJT]

I'm not so good at physics so I'll ask you people that really know. Everyine knows the surface of a planet, Kerbin or Earth or any other for that matter, is moving at a high rate of speed. I think earths surface moves 1000 mph? (That's my memory, correct me if I'm wrong.) It seems that when you launch a rocket straight up it shouldn't lose that velocity. It started out going whatever speed it was going to the east. Kinda like if you were in a car going 60 mph in a vacuum and you shot a bullet straight up it should travel just as far as you did laterally when it hits the ground. I know a greater radius means it would slow down but it seems like it jist stops...

[tomf]

Why do you think it loses that velocity? Most rockets are launched on an easterly orbit to take advantage of that rotation.

[tipsyMJT]

Well if you launch a rocket straight up, at least in ksp, the orbit has no arc, and it goes up and comes down in a much different place.

[Mr Shifty]

I'm not so good at physics so I'll ask you people that really know. Everyine knows the surface of a planet, Kerbin or Earth or any other for that matter, is moving at a high rate of speed. I think earths surface moves 1000 mph? (That's my memory, correct me if I'm wrong.) It seems that when you launch a rocket straight up it shouldn't lose that velocity. It started out going whatever speed it was going to the east. Kinda like if you were in a car going 60 mph in a vacuum and you shot a bullet straight up it should travel just as far as you did laterally when it hits the ground. I know a greater radius means it would slow down but it seems like it jist stops...

You can click on the velocity indicator at the top of your NavBall to switch it to Orbital speed. You'll notice that it shows about 180m/s when you're sitting on the launch pad. If you launch straight up (and ignore the air, which is also spinning at 180m/s near the ground), as you get higher and higher, the circumference of the orbit at that point also gets larger and larger, which means that 180m/s won't let you keep up with the spot on the ground that you left. If you fell straight back down, you'd hit to the west of your starting location because the planet would spin underneath you.

[tipsyMJT]

Thank you. That makes some sense

[Rune]

You don't lose the speed (well, you actually lose some to aerodynamic resistance, but disregard that), but you suddenly have to make a much bigger circumference in the same time the ground does. That is why you seem to start moving westwards if you go up.

[Jokurr]

This can also be represented mathematically if you are interested (neglecting loses due to drag):

Simple equation is that rotational velocity (usually measured in degrees per second or radians per second) is equal to velocity divided by radius. In this case your velocity is fixed at 180 m/s. As your rocket goes up, your radius from the center of Kerbin increases. Thus, according to that formula your rotational velocity must go down as radius increases. Since your rotational velocity is less than the surface of Kerbin, you appear to be moving westwards.

[tipsyMJT]

[E=Jokurr;432178]This can also be represented mathematically if you are interested (neglecting loses due to drag):

Simple equation is that rotational velocity (usually measured in degrees per second or radians per second) is equal to velocity divided by radius. In this case your velocity is fixed at 180 m/s. As your rocket goes up, your radius from the center of Kerbin increases. Thus, according to that formula your rotational velocity must go down as radius increases. Since your rotational velocity is less than the surface of Kerbin, you appear to be moving westwards.

[tipsyMJT]

Thank you for a mathmatical explanation. It helps me understand a little bit more.

[Mr Shifty]

You know, I'm rethinking this. I think in a vacuum, you'd land pretty much where you started at the timescales we're talking about, i.e. where the curvature of the planet does not come into consideration. The whole circumference increasing argument is moot because you're not moving at orbital velocities.

However, if the world was really small or had very low gravity, so the fall took an appreciable fraction of the world's revolution time, then I think you'd actually land to the east of your starting point because your velocity vector perpendicular to the ascent would always be, say, 180m/s, but the velocity vector of the launch pad stays the same total magnitude, but changes direction as the planet rotates, meaning its component perpendicular to your ascent becomes smaller and smaller.

We should test this on, say, Gilly.