So here I am sitting at work, having the opportunity to look at a full moon.
Of course my intelect has been so highly stimulated from this forum (ahahahah) excuse me, where was I? Oh yeah, looking at the moon.

How is it that the moon does not come crashing into the earth or go flying off into the void?

There is a constant pull on the moon from the earth, I know this.
And I know that because of the velocity of the rotation of the moon going around the earth that is akin to throwing a marble around a roultte wheel.
Forcing the moon/marble to the outside of the wheel.
But in this case, the moon has landed on an the most exacting calculation I can fathom to not come crashing into earth or fly away.

The more I think about this, the more it is seriously messing me up. I hope some one has a good awnser. I may have to go to the space forum on here for this one.

I mean, how does any planet in rotation around the sun stay in that EXACT LINE of rotation that it does not pass over into one side or the other.
Flying off further into space or gaining incredible momentum and crash into the sun.
Its infathomable to me.
I need serious help on this one.?!!! :(
Please tell me I'm an idiot and the awnser is soooo simple. Seriously.
Or you can just call me an idiot.
*sniffle* I can *sniff* take it. :(

After a bit more thinking, comparing the rotion of the moon to throwing a marble around the brim of a bowl would differ in two major ways.
The friction of air and contact of the marble and bowl having a sever impact on the momentum of the marbles speed causing it to come to rest much more quickly.
However, gravity is still there.As well as the present centrifugal force.

For the moon to stay in its exact plane of rotation, it weight would have to remain infinitely the same. Even one pound would have an influence on the amount of gravity exerted on the moon, causing it to come closer to the earth and yet it is constantly bombarded by meteors.

Is it possible that there is some knid of opposite force acting on objects, opposite of gravity, keeping all matter from imploding on itself?
I guess an anti gravity of some kind inherrent in all mass like gravity is.

This would help to balance out the objects rotation.
Like when you have a ping pong ball balanced on a cushion of air.
The gravity is still there, but the combination of the force of air/antigravity helps to balance it out even with all sorts of disturbances and wobbling.

I will have to continue thinking about this. :confused:

I mean, how does any planet in rotation around the sun stay in that EXACT LINE of rotation that it does not pass over into one side or the other.

planets do, thats why we sent all those mars probes a few months back, beacuse of our orbits that is the closest we will come to mars in 4 years

our orbits are slightly egg shaped , during 1 half of the year we get realy close to the sun and the earth spins faster making daylight savings, the moon is held to the earth by gravity but just too far for it to come crashing down

i just read thru wat i wrote, wat i meant to write up the top was we dont have perfect orbits

Thanks for your imput Vslayer.

our orbits are slightly egg shaped , during 1 half of the year we get realy close to the sun and the earth spins faster making daylight savingsThe earth doesn't spin faster. Your location is just at different angle.

moementum7,
A couple different question I think need to be answered

1) A planet 'gaining weight' won't make it tend to go any closer or further from the sun. All planets are in a constant state of freefall, and like the basketball and the bowling ball, all objects fall at the same speed regardless of weight. So basically, the earth could double in size and it would not crash into the sun (it would however bring the moon down on our heads).

2) The planets formed from a ring of 'stuff' (rock, dust, etc) that was around the sun (possibly before the sun itself completely formed). At every distance from the sun there is a velocity which will keep you in a stable orbit. Any of this 'stuff' that was going the right speed stayed in orbit, while everything else either crashed into the sun or left the solar system. This formed rings around the sun where the planets now are. This 'stuff' in these rings collided and stuck together, forming planets.

3) The moon is more difficult. It's possible that it formed like the planets do, but I think the current thought is that it was a part of proto-earth. Someone else may have a better idea here.

Thanks Persol.
Yes, you are right about the moons added mass not having anything ( in this particular eqaution) to do with the effects of earths pull.
It is more a matter of the mass of earth having the dominant effect.
Thanks for clearing that up.

Let me continue with the problem and keep it with the moon to help keep this problem as simple as possible.

The face of the moon never turns.
I am guessing that this may have something to do with the fact that perhaps one side of the moon is more dense than the other. Thus keeping that side always facing towards us.

How else would the moon have ever stopped spinning.
Once an object in space is moving, it stays moving until acted upon by another outside force.
I mean, to have the moon come to a complete stop(on its own axis) is quite interesting and connected to my earlier question.

If the moon is indeed heavier on one side, thus effected by earths gravity to such a degree of pull, unless being pushed away by some unseen force, like my air and ping pong theory above, the centripudal force alone does not quite add up.

What are your thoughts on that Persol.
Any theories?
Thanks for the input by the way.

The face of the moon never turns.
I am guessing that this may have something to do with the fact that perhaps one side of the moon is more dense than the other. Thus keeping that side always facing towards us.

How else would the moon have ever stopped spinning.
Once an object in space is moving, it stays moving until acted upon by another outside force.
I mean, to have the moon come to a complete stop(on its own axis) is quite interesting and connected to my earlier question.


You'd probably get more qualified answers in the Astronomy forum, but this is my understanding of it. The moon does wobble a little, and we can actually see more than 50% of it's surface from earth as it wobbles. Tidal forces from the earth have been slowing it's rotation down so it's synchronous to it's rotation around the earth. The earths gravity makes the moon slightly egg shaped, with the fat end near the earth. This makes it harder for this fat end to turn away, thus slowing the rotation down until the same side is constantly facing the earth.

Thanks shmoe.
Cool name.
You should change it to something cooler though like......Schmoementum7.
Got a nice ring to it don't you think. ;)
Any ways, I will try and clarify my question as I go along.
Basically what I am getting at is the presence of some force in nature that is the opposite of gravity.Not as potent as gravity, but there none the less.

For instance.
Imagine out in space, you have this massive object, lets just say a star.
Something with mass to present the force of gravity.
Now imagine throwing something like a ball, or(a planet) into its gravitational pull. Not throwing the ball directly at the star itself but just at the edge of its gravitational pull.

That object, if caught in its gravitational pull would have no choice but to contiually come in closer and closer to the star like a toy boat caught in the swirling water of your bath water as it goes down the drain.

It would be like having a black hole in space, and shooting a stream of light so perfectly at its outer influence of gravity that if the beam of light were caught at the exact distance neccessary from the holes center, it would find an orbit and make a perfect circle of light.

Is this possible, or does the law of physics dictate that the light would have to continue coming in closer and closer to the black hole.( like the toy boat)
Or would you sat that it is possible that if the short beam of light were travelling at the perfect range on the outside influence of the holes pull, that it would continue on that perfect influence of being inside the gravitational pull for a moment, then out of its pull, then back in, then back out, etc.

Unless there is some force that is actually pushing out from any object with mass, then the force of the objects intial inertia (its centripudal force)is not enough to keep it at this perfect balance of being pulled in and not being pulled in.
Just somewhere in the middle.

I hope someone is understanding this.
However, like Persol has mentioned, suggesting that there was perhaps a ring of mass of material all going at the same speed, to gradually, by its own gravitational pull would come together to form a larger object of mass.

Still, if the rate of speed at which the object is travelling is the only variable that is keeping any object in its current state of orbit, then even these rings of dust and gasses would vary in speeds as they collected.
I do not see how anything that is influenced by an objects gravity in space does not continue to be affected by its pull, or escape it.
But some how comes to rest on this perfect balance.
Not coming in, and not going out. Just sitting there on its orbit.
Ladee deedada.

How many times would it take you to throw a ball around a bowl, so that it would never stop going around and around?
Taking into consideration, air resistance and friction of the ball on the bowl, you might have to throw it a little harder.
Throwing it just hard enough so that it would not come down to rest because of gravity, and it would not fly out because of its inertia.
But a perfect balance in between. Allowing it to just keep going around and around and around and around...you get my point.

The inertia of an object is either enough to escape an objects gravitational pull or it is not, and thus continue to be acted upon by gravity and pulled in, or escape and contiue on its journey.
Not this perfect balance between pulled in and not pulled in.

There has to be some other force at work here.
Some force that is actually pushing out.
Something that is not dependant on an objects speed of rotation.
But a constant. :confused:

i know a reason why it would not crash into the Earth
the Earth pulls the moon closer, and it gets pulled away due to other forces. So SOME planets will have orbiting moons, others will have had moons crash into them. We wouldnt be sitting here if the moon had crashed into the earth, so we are obviously on one of the ones that the moon hasnt crashed into. Its probable at some time that the moon will crash into Earth or leave Earth's orbit, tis a matter of time really

If the moon were to crash into earth or escape its pull, don't you think it would have done so by now?
The forces of inertia and gravity are not something that contiuously happen at a consistantly slow level.
These forces are compounding.
Meaning that the rate of excelleration one way or the other is not something that happens over the course of thousands of years but virtually has the effect of happening within years.
This may sound slite, but in comparison to the the universe, is still exceptionally fast.
Compounding was one of the "Greatest concepts" known to man, according to Einstein.
If neccessary I will explain it, but I am hoping you all know what it means.
Once an object is acted upon by a force of gravity, it will continue to act on it at an accelerated( compounding rate) until maximum speed is reached or impact has occurred.
If the moon was going to crash into us,or fly off, it would have done so by now.
In my opinion anyways.

When you let go of a set of keys, they do not just hover there, enjoying its state of perfect balance between being let go and being acted upon by gravity.
It is acted upon gravity NOW.
And will continue to accelerate until maximum speed or impact.
No in between.
No constant orbit.
Unless there is some other force at work.

I have figured it out,
thanks to everyone.
Phew, I'm not crazy. :rolleyes:

just on the topic of moons does anyone know anything about the theory that 1 of jupiters moons was once a planet

Momentum:
I mean, how does any planet in rotation around the sun stay in that EXACT LINE of rotation that it does not pass over into one side or the other.
Flying off further into space or gaining incredible momentum and crash into the sun.
Its infathomable to me.

Had an astronomy teacher shut me the fuck up once- best way to learn and remember something so here goes:

Your use of a marble on a roullette wheel is a bit wayward- you introduce forces that do not exist in space, friction being one and those still stuck in aether are wrong.

There is, of course, a gravitational force between Earth and moon but the moon also moves at a finite speed around earth- (something these other posters here have said already); this motion creates a centripetal force on the moon which tries "yanking" the moon from Earth.
Gravitational force then equals this centripetal force.
Like and unlike balance each other. Perfect synchrony.

A broader explanation is Einsteinian and far more beautiful, I'm sure you've heard it. Spacetime is a fabric, and masses curve spacetime (though as to how exacty is still funny to me)- this curvature determines who pulls who where. The mass of the earth dominates that of the moon and so the moon orbits the Earth and not the other way around even though the moon curves its spacetime patch as well.
The sun's mass is equal to that of a hundred million planets so naturally the nine measly ones in our solar system would gravitate around it.

(small aside- if Jupiter were 8 times as massive it'd be a star. I wonder what our solar system would look like with these two stars challenging each other's gravitational pull on planets and other bodies)

The larger the object, the larger the curvature, the stronger the pull. This pull balanced by a centripetal force and voila- suspension.

Persol:
The moon is more difficult. It's possible that it formed like the planets do, but I think the current thought is that it was a part of proto-earth. Someone else may have a better idea here.
I like to think of there being no moon during the Cambrian period eons after proto earth, and a huge asteriod smashing a new ocean on its face- the Pacific.

And so, the chunk ripped out during impact that made the Pacific Ocean is our moon today.

VsLayer:
just on the topic of moons does anyone know anything about the theory that 1 of jupiters moons was once a planet
gendanken

No. Enlighten me.

Are you speaking of Europa?

And so, the chunk ripped out during impact that made the Pacific Ocean is our moon today.The basically seems to be the common view. I'm just saying that it is more difficult to explain an earth generated moon staying in orbit than it is to explain a condensing field of matter forming planets.

Persol:
The basically seems to be the common view.
Oh?

That Earth was already perfectly formed and functioning with life on it and no moon? I'm even going so far as saying that perhaps there was no moon and no Pacific ocean during the dinosaur age.

I've never heard this theory before.


I'm just saying that it is more difficult to explain an earth generated moon staying in orbit than it is to explain a condensing field of matter forming planets.
I see it viloently harder to explain the precise condensation of debris, at the precise point and at the precise time remaining loyal to an orbit while accreting.

Its far easier to think of a chunk of earth flying off into space.

the pacific ocean is too young to be the birthplace of the Moon.