I think i finally get it,, maybe

[KBMODIGITY]

After 684 hours playing this game I think I finally get how certain orbital mechanics work. When I started playing this game I knew absolutely nothing. I thought if you just went straight up you would get into orbit. Thank you Scott Manley for teaching me the error of my ways.

Well tonight I have my interplanetary mission to Jool with 6 probes with all kinds of science things ready to go. During the massively long burn phases I thought about why objects that are further away from the object that is their sphere of influence moved slower than others that are closer. Finally a light bulb went off in my head. I could be way off here but to me it seems that they don't actually move slower it is all relative. The further an object is from its SOI the further around the object it has to travel thus all objects more at pretty much the same speed around its SOI, possibly regardless of their own mass as well. I would guess then that the determining factor of a speed needed to reach orbit would be the mass of the object that is causing the SOI because of gravity.

I hope this makes sense and if it does can someone who is good with this stuff tell me if I am right or wrong. I love to learn more I just hate reading books. Also, please don't get all technical as then everything will go right over my head. Thanks in advance.

Edited June 22, 2014 by Vanamonde

[xcorps]

The further an object is from its SOI the further around the object it has to travel thus all objects more at pretty much the same speed around its SOI, possibly regardless of their own mass as well.

In NASCAR, cars on the inside of a turn drive with less velocity than cars on the outside but get through the turn quicker. Cars on the outside of the turn have a higher velocity, but get through the turn slower. So which one has more speed?

[Moss]

You're pretty much right.

[cpast]

No, it isn't just that a further-out object travels a longer distance per orbit. The further an object is from the planet, the slower the orbital velocity. If you double the radius of an orbit (thus doubling the length an object has to go to complete one orbit), the orbital period increases by a factor of around 2.8 (orbital period squared is proportional to semi-major axis cubed). Now, orbital velocity is a property solely of an orbit (and the craft's position in that orbit); mass of the craft has nothing to do with it, because at a given altitude, everything, no matter the mass, is subject to the same gravitational acceleration.

[Moss]

So which one has more speed?

Speed is the magnitude of an object's velocity relative to itself. Neither car therefore has more speed.

[cpast]

Speed is the magnitude of an object's velocity relative to itself. Neither car therefore has more speed.

...what?

No, that's not right at all. Speed is the magnitude of velocity. Period. Speed does not inherently imply any reference frame, let alone "inertial reference frame relative to which the object has zero velocity". If it was what you're saying, everything would have a speed of zero.

Velocity (and thus speed) only has meaning in a reference frame, which must be specified (this is normally implicit in everyday speech, but is *not* "frame following the object itself", because that's utterly useless for this purpose). For things on the ground, we normally use the surface of the Earth at that location as the reference frame. For things in orbit that are decidedly orbiting around only one body, we use (I believe) an inertial reference frame that translates with the center of mass of that body (in which case the reference frame does not rotate; incidentally, "reference frame Y does not rotate" does *not* require saying "does not rotate with respect to reference frame Z", because a reference frame just is or is not an inertial reference frame, and that property is not relative to any other reference frame).

Edited June 21, 2014 by cpast

[xcorps]

Speed is the magnitude of an object's velocity relative to itself. Neither car therefore has more speed.

Nossir. The car on the outside is moving faster, therefore it has more speed. A rocket with 2200 ms velocity is faster than a rocket with 1000 ms velocity. The velocity makes the orbit, not the other way around.

[Moss]

Oops- yeah, you're right. I got reference confused with vectors.

[Sandworm]

NASCAR /= space.

Space=nothing and nothing=space. There aren't any earthbound equivalents to orbital mechanics. We can talk of spinning ropes with weights, but there isn't anything that truly mimics the force of gravity between spheres in space.

Cars on a track are 'pulled' inwards by a force generated due to a difference between the angle of their wheels (the metal bits) relative to the road underneath. A car on the outside of a turn, a wider radius, has a lesser difference between wheel and road. This resulting in higher possible speeds, but the car must travel a further distance to complete the turn. On a nascar track this difference is slight, less than a few meters. The real speed comes from height. The cars on the outside of a nascar-style track are physically higher than those on the inside. The outside cars turn this potential energy (height) into greater speed as they drive downhill exiting the turn.

Think of how fast a car would move if you let it coast from the top of a nascar turn towards the inside directly (ie 90* to how the cars move in a race). That momentum is the same energy that a racer gets exiting a turn from the outside lane.

Edited June 21, 2014 by Sandworm

[xcorps]

NASCAR /= space.

Space=nothing and nothing=space. There aren't any earthbound equivalents to orbital mechanics. We can talk of spinning ropes with weights, but there isn't anything that truly mimics the force of gravity between spheres in space.

I wasn't talking about space, I was talking about speed. And NASCAR = speed.

[Moss]

Both are examples of circular motion.

[FleshJeb]

Conservation of Energy is key here:

Without outside inputs such as thrusts or gravity assists, the energy of the orbit always remains the same.

When you're headed out to Apoapsis, you have a lot of Gravitational Potential Energy, and are thus moving pretty slowly: http://en.wikipedia.org/wiki/Potential_energy#Gravitational_potential_energy

As you fall back in towards Periapsis, it turns into Kinetic Energy and you go faster:

http://en.wikipedia.org/wiki/Kinetic_energy#Kinetic_energy_of_rigid_bodies

A clock pendulum is a good example of this.

See also this:

http://en.wikipedia.org/wiki/Vis-viva_equation

[cpast]

That works for elliptical orbits, but less so for circular - two different circular orbits have different orbital energies, and it's not immediately obvious that the higher orbit has lower speed.

[No one]

In a circular orbit, the reason why an object in a higher orbit is slower than an object in a lower orbit is because there is less gravity when you're farther away from the planet/star/moon.

Edited June 22, 2014 by No one

[Roastduck]

just gonna leave this here:

http://en.wikipedia.org/wiki/Angular_momentum#Conservation_of_angular_momentum

[cpast]

Again, only explains speed differences in elliptical orbits. Angular momentum is *not* the same between two different orbits.

[Lheim]

An object that's closer to the planet it's orbiting has to move faster tangentially to avoid slamming into the planet - say it's only 50 klicks up, and only has that far to 'fall' before it might hit the surface. To get round the curve of the body, it has to motor much faster than something significantly higher up.

Also, gravity does a weird thing: it decreases inversely to the square of the distance. An object a hundred times further out would feel 1/10000th the gravity pull. So if it did move as fast at that height.. it would just plain darn escape.

Edited June 21, 2014 by Lheim

[roosterr]

This is a great post, and the most productive use of the "game". You sound like me beginning two years ago. I dont have time to provide you with links, but this game turned me on to gravity (the heart of orbital mechanics). YouTube is your friend, there are lots of video explanations about gravity out there. You would think gravity is a simple as an apple falling from a tree, but there is a lot more to it. It is simple, yet can be complex, and surprisingly fascinating. Once you have a grip on that concept, check out something called "Lagrange Points", which are like magical loopholes in the laws of gravity that exist around earth and our solar system, AND they will make sense to you once you understand gravity and orbital mechanics.

Lastly, once you have the above understood, look into orbital mechanics vs. quantum mechanics, oh baby, talk nerdy to me

I would have never guessed that I would ever find any of that interesting, but KSP opened that door, as well as other great things.

[KBMODIGITY]

I realy don't understand why just something that popped in my head as truth for physics which I said could be totally bunk,, yet now all these people fighting

[KBMODIGITY]

can anyone please read the original post and tell me if i'm right or wrong? that's all I wanted,, and like I said,, no intense explinations. lamens terms,, god forbid

[maltesh]

can anyone please read the original post and tell me if i'm right or wrong? that's all I wanted,, and like I said,, no intense explinations. lamens terms,, god forbid

It is incorrect. The object in the higher circular orbit definitely has a lesser speed, relative to the object being orbited, than the object in the low circular orbit. KSP's Orbital Velocity readout is not misleading you about this.

[rkman]

I could be way off here but to me it seems that they don't actually move slower it is all relative. The further an object is from its SOI the further around the object it has to travel thus all objects more at pretty much the same speed around its SOI, possibly regardless of their own mass as well.

You're off, it is both:

Objects further out do have a lower orbital speed (speed is absolute, not relative) because gravity is less the further out from the central body, so the centrifugal force needed to balance out the force of gravity is smaller, so the object needs to move slower.

Besides that also the orbital path is longer.

[Vanamonde]

This thread has been moved to Science Labs, since it's a science question. And with regard to some removed posts, please express yourselves on this forum without insults and profanity.

Edited June 22, 2014 by Vanamonde

[Dkmdlb]

Objects further out do have a lower orbital speed (speed is absolute, not relative) because gravity is less the further out from the central body, so the centrifugal force needed to balance out the force of gravity is smaller, so the object needs to move slower..

I'm sure you didn't mean it in this way, so forgive me in advance, but orbital mechanics can get confusing, especially early on in the learning curve, and there is a tendency to put the cart before the horse in the way you inadvertently implied. It's not that higher orbits cause slower speeds, it's that higher orbits are only possible with slower speeds; anything moving faster escapes from the parent body within a very short time, so we won't ever see a faster moving body out in a high orbit. The more intuitive corollary to this is that objects in very low orbits move much faster not because the high gravity causes them to move faster, but because anything moving slower falls back down to the planet. The higher speed is not the result of the low orbit, but the cause of it.

(PS I used scientific terms like "speed" in a sloppy way).

[KBMODIGITY]

OP here,, can someone not noob it up for me??,, just want the basics,,, yet it seems like I opened a huge can of worms. ughh. I see all these people back and forth with each other on who's right and who's wrong. None of it answers me question. I would like to know the answer to my OP but I think its best to close this thread as I have seen too much head butting over it. ANY MOD PLEASE CLOSE THIS AT THE REQUEST OF THE OP. thank you.

I only wanted to learn, not cause conflict. Thank you all that posted. I read and somewhat learned in me limited way (why I asked for simple terms). TY again. but I cannot see a thread going on causing this much conflict. goodnight.