0 gravity

It seems to me that there would be no reason, GR or Newtonian that prevents there from existing a point in space where there is no NET gravitational force. If one could pause the universe and calculate the gravity from EVERY peice of matter in the universe, there could exist somepoint in which there is no NET graviational force.

-AntonK

 

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Regarding zero gravity between two masses, what prevents our moon from being pulled to the earth, a larger more massive object with greater gravitational force? In essence, the moon itself has an effect on the earth, pulling the tides of our oceans. Just curious what keeps the moon in space, and why the earth's gravitational force does attract other smaller objects into it's orbit as Jupiter does with larger ones (or does it?). I heard we actually DO have 2 moons, one most people don't know exists.

 

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I totally agree. That's the point I was trying to get across to blindman.

 

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Theoretically, yes, zero net gravity is possible, but i am doubtful that such a position is space exists. The universe is not static, and therefore even if such an equilibrium did exist, it would not be in a constant location. Not to mention, calculating this position would be near impossible.

And about the question regarding why the moon stays in orbit around the Earth. Just like any satellite, if an object has enough tangential velocity, or that which equals the velocity needed to create a centripetal force equal to a massive body's gravitational field, orbit is possible. A satellite has a net acceleration to the CENTER of its orbit. If it also has sufficient tangential velocity, it will 'fall' around the Earth eternally.

Think of a cannon that shoots a ball horizontally. That cannon ball will curve out a parabolic path due to gravity and its tangential velocity to the Earth. If you shot this cannon with enough force, the Earth would actually 'curve away' from the ball as it traveled due to the fact that the Earth is a sphere. With enough velocity, the cannon ball would actually fall all the way around the earth, (neglecting air resistance of course).

 

I know they told you in a basic chemistry class (or wherever) that all vibrational motion stops at absolute zero, but this isn't the case. Quantum physics tells us that there will still be some vibrational energy in a system, even if cooled to absolute zero; this energy is called the 'zero point energy'. As a system approaches absolute zero it does not approach zero energy; the energy of the system will approach a limit, and the limit will be the zero point energy. It is the energy of every particle in the system being in its lowest quantum state. There will always be some motion, even at absolute zero.

Also: I agree that you could have a point of zero net gravity, but wouldn't it be merely a one-dimensional point?

 

I never really thought about it until you brought it up, but yes this point probably would have to be of one dimension.

 

If you are sitting there measuring the gravity, you will be exerting your own gravitational field.

 

With regard to the point of no NET gravitational pull. I think it would be a suitable time to remember this point:

I agree in that I think it's theoretically possible to have a point where there is no net force. That is a very different concept than no force.

Don't forget that energy as well as matter generates a gravitational field. So every photon would have to be taken into consideration!

 

anyone here ever heard of the Bose-Einstein condensate?

Scientist were able to cool some atoms down to only a few billionths of a degree above absolute zero!

intresting read if you want....

http://www.harvard-magazine.com/issues/mj99/right.light.html

there are lots of other sites about it, so I am sure you can find a lot of info.

They used lasers to slow the motion of atoms.... thats pretty smart

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Its known as the Lagrange Point - where the two opposing gravities cancel each other out.

http://map.gsfc.nasa.gov/ContentMedia/lagrange.pdf

Acrobat Adobe 5 is required to read it.

 

As sargentlard said, if scientists have reached a point where they can stop all motion in a given place there can't be any engery, and in turn be no heat.

 

we can never reach 0 because there is always some source of heat somewhere, and even though its extremely miniscule, that heat is always there no matter what

 

If you are in space, your "weightless" right? Well thats because you are always falling, that is what gives you "weightlessness". So yes, gravity is absolutely positively everywhere.


Later
T

 

Falling only gives the illusion of weightlessness. Anything with mass that is influenced by gravity has weight, but if a mass is in this "Lagrange Point" it will not have weight because gravity is 0.

 

It is not the act of falling that creates weightlessness. To say the reverse, the feeling of weightfulness is something pressing against your feet, which in turn press against your ancles...

You could look at it from the head down as well, anyway I hope you get the picture.

Note to physicists: Please don't point out the exacts of reaction forces etc, I'm just pointing out the net effect for eases sake.

 

You refer of course to Newton's Action and Reaction

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You are weightless in space..........

 

Yes, the Earth has at least 2 moons. the second moon being a captured asteroid called Cruithne.
This asteroid, or Near Earth Object which doesn't orbit round the Earth as such, but orbits in a harmonic resonance with the Earth, periodically reversing it's course and appearing to retrace its motion.
animation
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The "second moon" is not in orbit around the earth but in orbit around the sun.. Nether is this orbit stable. It is unknown how long this object will remain in this chaotic orbit.

We don't even know if is a piece of space junk or not... A pixel or two on a radar screen dont mean much.

 

First of all humans have never been able to explain gravity.
We have Newton and General relativity. With this we can calculate the motion of objects. But it does not explain gravity it just tells us what it sort of looks like in time.

Second.. Space does not equal weightlessness. Orbits equal weightlessness. If I build a tower a thousand km high. I could climb all the way to the top without even feeling the slightest drop in gravity. Playing on a trampoline I could watch the space shuttle pass underneath with its weightless crew. You need a tower 32000 Km high before your weightless and thats because the centrifugal force.. If it was built at the poles we could climb up past the moon and still have fun on a trampoline.

Weight and mass are two different things. Mass is almost constant (especially at our human slowness), weight changes all the time. Just jump up and down on a scale and watch your weight change.

And with Newton and Einstein. We have only one way to measure gravity. That is via the motion of objects in time. If its says ZERO the is no reason to believe there is any gravity there. Thing don't have to make sense to be true.

 

Yes, that's more or less it- a third 'moon' was was discovered but it turned out to be an old Saturn V booster:
http://news.bbc.co.uk/1/hi/sci/tech/2253385.stm

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