Try to jump so high that you fly right off of the Earth into

[Min3mat]

i think that the lightbulb year is cool now that i know what it means! :D

[PauloMorfeo]

...
The escape velocity for the surface of the Earth is about 11 km/sec. ...

For start, velocity is relative. I supose you mean the velocity of the object relatively to earth.

If the velocity is constant, any velocity greater than 0, will continually move the object away from earth.

If the velocity is the result of an inpulse and is not maintained afterwards, like the velocity in the begining of a jump, in theory, you would never escape the gravity of the earth. The gravity field is infinite and it would eventually slow down the object and eventually pull it back no matter what. In practice, the object would most likely be strongerly atracted by another mass out there, never to return (or maybe hit the boundaries of the universe?).

Then, how does the satelites remain up there and don't fall down onto earth? I'll see if you guys figure that out.

[IMSabbel]

...
The escape velocity for the surface of the Earth is about 11 km/sec. ...

For start, velocity is relative. I supose you mean the velocity of the object relatively to earth.

If the velocity is constant, any velocity greater than 0, will continually move the object away from earth.

Well, thats kind a retarted way of looking at it, because a constant velocity while moving out of a gravity well requires an external energy source and thus isnt in any way a constant state. To bring it up here is a very cheapass way to be a smartass.

If the velocity is the result of an inpulse and is not maintained afterwards, like the velocity in the begining of a jump, in theory, you would never escape the gravity of the earth. The gravity field is infinite and it would eventually slow down the object and eventually pull it back no matter what.

Omg. Please tell me that you havent finished junior highschool, or did newton never invent calculus where you live? You are just as bad as those free energy from magnetic dipol nutheads you can find in the internet.

A hint: Maybe you come to this (wrong) solution by trying to be clever and integrating over the 1/r potential and finding it to diverge.
Sorry boy, you can use it directly, (or integrate over the 1/r^2 force, smae thing).
Result: if your object m moves with a speed of v, and E_K=1/2 m v^2 is greater than the E_P=-G M m/ r, than it WILL continue forever with a positive relative velocity. (which happens to convieniently be the 11km/s the original poster spoke of, just instert r=6000km , the universal gravity constant and the mass of earth)

In practice, the object would most likely be strongerly atracted by another mass out there, never to return (or maybe hit the boundaries of the universe?).

True for the first part, for the latter part... well, yeah right. just like i fall over the edge of the sea when i take ship over the ocean.

Take a look at some cosmology topics, including some older, outdated stuff about open/closed universe depending on total mass of matter (i say outdated because the newer stuff depends almost completely on the influences of dark energy and matter (epecially former), which are a bit too sophisticated for you, i guess)

Also, take a look at jeans instability criteria: gravity isnt really the sucker that pulls everything together everytime, you know.

Then, how does the satelites remain up there and don't fall down onto earth? I'll see if you guys figure that out.

Wow, im not sure if i can solve that mystery, scienceboy. But what _I_ am MUCH more interested about is what bullshit solution YOU seem to have (because i cant really imagine how you have to rape math with your logic for the twobody problem to be solveable)

/me slightly annoyed by another 13 year old you tries to make a "i know stuff" impression on the internet.

[Zoombie]

Satilite's stay in orbit because they orbit aroudnd the earth, balencing there intital velocity against the gravitationall pull of the planet and there for, staying in the path wanted. This is of course an educated guss based off what i know (not as much as i would like) and basic logic.

[Delta]

Zoombie is right.
Satelites stay in orbit because they are cntinously falling towards earth, with the difference that their horisontal spped is big enough to counter the gravitation of earth.



the gavitation is trying to pull the sat. down, and the horisontal speed is trying to move it in a straight line out in space, the combination of the two velocities gives the tangent that keeps the sat in orbit, continously falling at a constant speed not getting any closer to earth.

[munch]

the gavitation is trying to pull the sat. down, and the horisontal speed is trying to move it in a straight line out in space, the combination of the two velocities gives the tangent that keeps the sat in orbit, continously falling at a constant speed not getting any closer to earth.

"the tangent"... only assuming a perfectly uniform gravitational field and zero eccentricity in the orbit ;-)

Munch

PS nobody answered the "why don't they fall back to earth" question yet - he's envisaging you blasting off directly away from the centre of gravity I think (very hard to do on a rotating planet - polar launchpad anybody)? Or maybe that's the answer he's looking for - that you don't blast off at a normal, so that when you fall back down you miss the earth and overshoot and fall back "down" (erm "up" I guess!) and miss again and fall back down etc. assuming you lose no energy, you'll keep going for ever. If you fail to miss the earth on your way back down, well then you're not in orbit. This reminds me of Hitchhikers: to fly, throw yourself at the ground and miss =) Well it's not really flying, but that's how you get into orbit innit?

[PauloMorfeo]

...
PS nobody answered the "why don't they fall back to earth" question yet ...

Well, i'm not entirely sure as i didn't understood 100% everything it was told but i think that Zoombie tried to and Delta did.

The lack of specific english knowledge may be a problem here...

Pick up up bucket full of water and spin it round up and down around you fast enough. When the bucket is at the top, up side down, the water does not fall because it is beeing thrown to the outside of the circle by a force that in portuguese is called centrifuga...
(That's what Delta explained but i think this is easier to understand)

The satelites are stable around the earth because they are going round around it in a ~perfect balance between getting pulled by earth's gravitational force and beeing thrown out by the "centrifuga" force.

Tell me, IMSabbel, how old are you then, ho most knowledgeable lord of science?

[Gurkha]

actually dentrifugal force doesn't really exist, it's the equal-and-opposite reactionary force to centripetal force, which is pulling it in (or so I understand), thus keeping the water in it's original place in the bottom of the bucket. The fact that you're not letting go of the bucket causes the bottom of the bucket to 'turn' the mass of water and keeping it accelerating inwards, this has an equal and opposite reaction (Newton's second law) which stops it actually going inwards.

Now, for a satellite. Imagine it's motion is a straight line:




now, imagine a force pulling down on it (only down, not affecting it's horizontal movement):



it's movement is now curved (oh, and imagine it's flying over the earth)



But, the earth is round, and it gets drawn closer to the earth the earth slips further away:



And since the earth is falling away from the satellite and the same speed as the satellite is falling towards it the satellite never reaches the earth. The speed that the orbiter moves is key to it's orbit, things moving at different speeds have to be at different heights - it's almost impossible to be at exactly the right height for your speed, that's why things like the ISS have to make slight corrections with thrusters, (that and the fact that the ISS is in Low earth orbit and brushes on the atmosphere, slowing it down.

voila:


-Gurkha
(hey looks like I learnt something this year)

edit: hmmm, ok, my diagrams aren't coming out, that's not good (replaces text-based images with pictures)

[AF]

About the edge of the unvierse thing, the bunvierse is a symetrical dodecahedron, you cant exist outside the universes boundaries because in doing so you make it so that there is a possibility of something existing in that location. If it is probably that something could exist there then space will exist in that place. The edge of the unvierse is simply where the probability of a particle or virtual particle existing becomes zero. So no matter how hard you try you can never reach or surpass the boundaries, for one you couldnt emit any force of any kind to get anywhere near it.

[aGorm]

To think a few bears can cause all this educated disscussion...

Long live aGorm

[AF]

that and the fact that the ISS is in Low earth orbit and brushes on the atmosphere, slowing it down.

Ha, if the Americans hadnt used shoddy thermal shielding tehcnology and other countries hadnt scrapped their own shuttle projects and the ISS was in a much higher orbit and tripple the mass, then the possibility of it falling to earth may be a threat. Likelihood of it hitting anyone though is slim.

Did you see mir when the russians abandoned it?

Oh and where were the bears aGorm =s

[aGorm]

Amazing how you can miss spell Beer after a few bears...

aGorm

[Gurkha]

no, the probability of it hitting earth is extremely slim to zero, it knows where it is in relation to it's proper orbit and corrects with thrusters, it's not like it's losing several meters a day or anything, on a tiny, tiny bit. Just enough that it needs to correct itself occasionally.

At the moment I can't actually find any evidence of this and am working on my hazy recollection of what my physics teacher said 2 years ago... But, since, as a physics student, I'm infallable, you should trust it anyway

-Gurkha

edit:
ah, 3 sentences from the Wikipedia ISS page:

The space station is located in orbit around the Earth at an altitude of approximately 360 km (220 miles), a type of orbit usually termed low Earth orbit. (The actual height varies over time by several kilometres due to atmospheric drag and reboosts. The station, on average, loses 100 meters of altitude per day.)

Apparently it does lose several meters per day, yikes!

[AF]

Yes you are correct, it is very hard to achieve the exact speed as you'll always be out by just a tiny bit be it nanometres per second etc. This is especially true of low orbit satellites that might be slowed down by the very top layers of the atmosphere or far out satellites that might be going a bit too fast.

[Dragon45]

I dont agree with the assumption that you would need an infiite escape velocity to escape a black hole... black hole's gravitational fields change depending on their size, so we canthen assume that black hole grav fields are finite strength, a finite quantity. All you need is something theoretical (tachyon mebbe?) that travels at a sufficient velocity to escape a black hole.

[Metaltrash]

Well since you can't be faster then light you have a problem...

And as sone as you are so far in that your protons and neutrons go to the big ball in the middle and the elektrons stay outside (you're already dead ..) u have no chance of escaping a black hole.

And about the orbating, look at the planets, do they have bosters so they don't get pulled in by the sun?

Every thing is relativ.

[aGorm]

What the hell... This is still going??!??

aGorm

[Min3mat]

i'm dropping physics next year :D

[mother]

I dont agree with the assumption that you would need an infiite escape velocity to escape a black hole... black hole's gravitational fields change depending on their size, so we canthen assume that black hole grav fields are finite strength, a finite quantity. All you need is something theoretical (tachyon mebbe?) that travels at a sufficient velocity to escape a black hole.

IANAAP, but, I have the following thoughts:
-Assuming that 'inside the event-horizon' is 'inside a black hole,' then anything with positive mass ain't getting out. This is because it would need to achieve >c to escape. I think what's confusing the discussion is the density issue... From the event horizon on in, even photons cannot escape. At the center there is a singularity... Which is whatever the current mass of the BH is (1mg, or 1x10^30 kg) over a 0x0x0 volume... So it has infitite density... At least theoretically :)
-And yes sir... a tachyon - which to remind people is a theoretical particle that moves faster than the speed of light- could maybe achieve sufficient velocity [>c] to escape the event horizon of a BH

The thing your poking your finger at is the disconnect between newtonian and quantum physics... See newtonian physics just doesn't work with a blackhole.
[Its the good old 'Divide by Zero' error]

[SwiftSpear]

I dont agree with the assumption that you would need an infiite escape velocity to escape a black hole... black hole's gravitational fields change depending on their size, so we canthen assume that black hole grav fields are finite strength, a finite quantity. All you need is something theoretical (tachyon mebbe?) that travels at a sufficient velocity to escape a black hole.

You don't need an infinate velocity to escape a black hole... you need a velocity > 0... The problem is, in order to produce a velocity > 0 from in a black hole requires an infinate ammount of energy. That is assuming your netrons haven't already bunched up all together compressing your mass to that of a virus.