Gravity theory has a bug?

  • Thread starter meckano
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  • #1
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Main Question or Discussion Point

For those that reply just to trash others, go find another thread.... please!

I understand that gravity warps space; I also understand that the moon is revolving once per approx. 27 days.

1)
If the moon is going in a straight line and gravity is warping its 'straight' path into an orbit, then it is not rotating; and it would rotate still, if it were rotating when it got caught into an earth orbit.
2)
They say that the far side of the moon is heavily cratored because of the more massive make-up of that side, and techtonic motion can not occur.

So, I am to believe that the moon had NO original rotation?
And that the more massive side just happens to be away from the earth? (it's centrifugal 'outside'.)
- too much coincidence!

Picture this:
A string attached to a bucket with some water.
Floating in the water: a hollow ball with a weight attached to one point inside of it.
Now, spin the bucket with the string.
The ball, which can move freely as it floats on the water, will 'float' with its more massive (weighted) side towards the centrifugal 'outside'.

so, the water is letting the ball orient itself easily, as is space allowing the moon to, and
the weighted side of the ball is like the more massive side of the moon.

Now that sounds, and seems, much more like what is going on.

Then, ofcourse, comes my 'not liking' how gravity is being explained; and as they still can't figure it all out, maybe I have a good point worth looking at.
... more on that, reply dependant.

Cheers.
 

Answers and Replies

  • #2
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Several of your assumptions are incorrect.

The far side of the moon (not the dark side..) is more cratored, because the near side is more shielded by the earth.

If two bodies orbit close to each other, and have some original rotation, then over time the tidal forces of gravity will dissipate the original separate rotations. So neither of your "coincidences" are so.
 
  • #3
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oh.

I got my information from here:
http://antwrp.gsfc.nasa.gov/apod/ap070225.html

But that still does not explain conflict between:
1)
That gravity changes the path of the moon, and
2)
It's said that moon revolves once per 27 days.

they can not both be true.

some change in: which 50% of the moon is facing earth , would have been noticed over the years.... or atleast calculated by now.
 
  • #4
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Yes, they can both be true. In fact, they are. And I already just explained why it isn't a coincidence. Eventually all the friction of the earth's tides moving around our planet, as they are dragged by the moon, will also cause the earth to stop rotating relative to the moon.
 
Last edited:
  • #5
vanesch
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So, I am to believe that the moon had NO original rotation?
And that the more massive side just happens to be away from the earth? (it's centrifugal 'outside'.)
- too much coincidence!
This is like saying: Am I to believe that the wheel of a car had exactly the right rotation in order for it to correspond to the speed of the car at its circumference ? Too much coincidence!
 
  • #6
HallsofIvy
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oh.

I got my information from here:
http://antwrp.gsfc.nasa.gov/apod/ap070225.html

But that still does not explain conflict between:
1)
That gravity changes the path of the moon, and
2)
It's said that moon revolves once per 27 days.

they can not both be true.

some change in: which 50% of the moon is facing earth , would have been noticed over the years.... or atleast calculated by now.
You seem to be under the impression that "gravity changes the path of the moon" means that gravity is constantly changing the path of the moon- so that it never follows the same path (relative to the earth) twice. That's not correct. "Gravity changes the path of the moon" means that gravity changes the "natural trajectory" of the moon from a straight line to an ellipse. There is no reason for that ellipse to change.
 
  • #7
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ok,
here is yet a 3rd thing that must be true then:

The poles of the moon must be perfectly lined up with those of earth.

3 things is.... too much coincidence.
 
  • #8
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Trajectory --- path

If we put something in orbit around earth, a ball, without spin; would the same face always be towards earth?
 
  • #9
2,006
5
The poles of the moon must be perfectly lined up with those of earth.
I think you'll find this is not the case. (Is it a coincidence that these three things are all coloured blue: the sky, humans, and the sea? No, because the sea just reflects the colour of the sky, and humans aren't blue.)

If we put something in orbit around earth, a ball, without spin; would the same face always be towards earth?
Eventually, yes.
 
  • #10
russ_watters
Mentor
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ok,
here is yet a 3rd thing that must be true then:

The poles of the moon must be perfectly lined up with those of earth.

3 things is.... too much coincidence.
Well that one isn't even true and the first two aren't a coincidence any more than the fact that it is bright out when the sun is up. One is caused by the other.

You may find it easier to understand tidal forces if you consider forces separate discrete particles on opposite sides of the moon instead of thinking of the moon as a single point mass.
 
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  • #11
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I think you'll find this is not the case. (Is it a coincidence that these three things are all coloured blue: the sky, humans, and the sea? No, because the sea just reflects the colour of the sky, and humans aren't blue.)



Eventually, yes.

i may find it, depends where i look, thought i was looking here.
thanks anyways, have a good day?
 
  • #12
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Well that one isn't even true and the first two aren't a coincidence any more than the fact that it is bright out when the sun is up. One is caused by the other.

You may find it easier to understand tidal forces if you consider forces separate discrete particles on opposite sides of the moon instead of thinking of the moon as a single point mass.
a mentor saying that something isn't true, is not mentoring.

we need to shake the government up a bit and get the schools working right.
 
  • #13
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well, it's been a fun game of merry go round; i'm getting off now.

ta ta
and grand futur, 'in the box'.
 
  • #14
765
15
Several misconceptions here:
I also understand that the moon is revolving once per approx. 27 days.
I take it by revolving you mean orbiting the earth.
1)
If the moon is going in a straight line and gravity is warping its 'straight' path into an orbit, then it is not rotating; and it would rotate still, if it were rotating when it got caught into an earth orbit.
no the moon is not rotating, one side always faces the earth (within a human lifetime), it has run out of rotational energy a long time ago. Also the moon formed by a large impact between the earth and a mars sized projectile (this is the current scientific concencus at least), in fact the impact was so large the earth might have looked like an apple with a massive bit taken out of it, cutting right down possibly as far as the core! I don't believe the moon just got caught in our orbit without any collision taking place.
2)
They say that the far side of the moon is heavily cratored because of the more massive make-up of that side, and techtonic motion can not occur.
As far as I am aware the mass of the moon is homogeneously distributed, give or take some anomalous variation. If the moon were more massive on its far side, I fail to see how that would occur, gravity being an attractive force and all, it would make much more sense if the massive side were closer to us (your argument with the bucket of water is flawed for reasons I cannot be bothered to go into). The only thing I can think of to possibly explain this (assuming for a second that it's actually true!) would be that the additional meteorites on the far side effectively increase the average density, possibly by a combination of metamorphosis into higher density mineral phases of the target material associated with the shock of an impact and the addition of high density meteorite material.
As for using this as an argument for tectonic motion not occuring, you are clearly very far out of your depth, I wouldn't go there if I were you.
 
  • #15
chroot
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a mentor saying that something isn't true, is not mentoring.
When a user produces some nonsense statement out of thin air -- with no explanation of how or why they were led to make that statement -- there's not much 'mentoring' that we can do. You stated a falsehood matter-of-factly, and it it was rejected just as matter-of-factly.

we need to shake the government up a bit and get the schools working right.
Does this mean you're trolling? Sure seems like it.

- Warren
 
  • #16
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Misconceptions upon misconceptions.

The moon orbits the earth every 28 days, keeping one face towards the earth which means that it also rotates on its own axis in 28 days.

Use a globe and a golf ball and you'll see it's true.

Phew.
 
  • #17
765
15
Misconceptions upon misconceptions.

The moon orbits the earth every 28 days, keeping one face towards the earth which means that it also rotates on its own axis in 28 days.

Use a globe and a golf ball and you'll see it's true.

Phew.
If you attached your golf ball with a solid rod to your globe and then span your globe then the gulf ball would show only one face to the globe. Is it fair to say that the gulf ball is rotating? I don't think so, I could be wrong, one way to check would be to see if there were any Coriolis acceleration on the moon, I don't think there would be.
 
  • #18
chroot
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If you attached your golf ball with a solid rod to your globe and then span your globe then the gulf ball would show only one face to the globe. Is it fair to say that the gulf ball is rotating?
Are you kidding? If you connect the globe and the golf ball rigidly, and then rotate one, how can you not also rotate the other?!

Draw a little arrow on the top of the golf ball, and watch the direction of that arrow as you turn the globe. Observe that the arrow changes direction constantly as you turn the globe, and makes one complete rotation as you turn the globe through one complete rotation.

I don't think so, I could be wrong, one way to check would be to see if there were any Coriolis acceleration on the moon, I don't think there would be.
There certainly would be Coriolis forces on the Moon, but they will be much smaller than the Coriolis forces on the Earth. The Earth rotates once each day; the moon rotates once every 28 days.

- Warren
 
  • #19
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Absolutely. There's an easy way to check, you go to the moon and you'll get a sunrise 14 days after sunset and sunset 14 days after sunrise.

Or you could do it with the globe and golf ball.
 
  • #20
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Since Coriolis forces were mentioned, a good check might be to look up how oblate the moon's shape is. The oblateness of earth is such (due to the otherwise inevitable flows of material) that the effective gravity (the combination of Newtonian gravity and Centrifugal force, the latter being the most absolute measure of rotation) is constant over most of the surface.
 
  • #21
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Correction:
The moon's rotation, for those that believe there is one for every orbit, has to be perfectly perpendicular to it's orbital path; and not parallel to the earth's poles. ( I knew something sounded wrong when I wrote it. )
 
  • #22
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Chroot, you obviously are not grasping this thread.

Your last post shows Clearly that you also don't know the difference between a gravitationally caused orbit, and rotation about ones own axis.

You do, however, have the same question I do, but are not willing to admit your own shortcomings.
Say after me:

I ... Don't ... Know ... 'THE' ... Answer ... but ... I ... know ... what ... I've ... been ... taught.

and we'll go from there, together, as learning, curious humans.
we'll speak literally with each other, using figures of speech and analogies to try to get our points across; but always relying on the 'being literal' part for clarity.
We Will Not insult from inside the box, using the level of ones own education as the only right to the podium.

If gravity were figured out, then this thread would not be here, i'd be reading the answer in a book.
- Now, we go back to square one, as the saying goes, and see what we missed.

Here, today, in this thread, we are looking at ORBITS, REVOLUTIONS, a bucket test, and a golfball test.
 
  • #23
HallsofIvy
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Several misconceptions here:
I take it by revolving you mean orbiting the earth.

no the moon is not rotating, one side always faces the earth (within a human lifetime), it has run out of rotational energy a long time ago. Also the moon formed by a large impact between the earth and a mars sized projectile (this is the current scientific concencus at least), in fact the impact was so large the earth might have looked like an apple with a massive bit taken out of it, cutting right down possibly as far as the core! I don't believe the moon just got caught in our orbit without any collision taking place.
On the contrary, the moon is rotating. It rotates on its axis once every 27 days- the same periods as its orbit around the earth.

As far as I am aware the mass of the moon is homogeneously distributed, give or take some anomalous variation. If the moon were more massive on its far side, I fail to see how that would occur, gravity being an attractive force and all, it would make much more sense if the massive side were closer to us (your argument with the bucket of water is flawed for reasons I cannot be bothered to go into). The only thing I can think of to possibly explain this (assuming for a second that it's actually true!) would be that the additional meteorites on the far side effectively increase the average density, possibly by a combination of metamorphosis into higher density mineral phases of the target material associated with the shock of an impact and the addition of high density meteorite material.
As for using this as an argument for tectonic motion not occuring, you are clearly very far out of your depth, I wouldn't go there if I were you.
 
  • #24
24
0
Misconceptions upon misconceptions.

The moon orbits the earth every 28 days, keeping one face towards the earth which means that it also rotates on its own axis in 28 days.

Use a globe and a golf ball and you'll see it's true.

Phew.
If gravity is causing an attraction between the 2 bodies, that would be the truth.
If gravity is changing the spacetime straight path of the moon, then the moon has no revolutions.

Someone has stated that the moon did revolve, and that it nolonger does. That statement means that gravity is changing the straight path of the moon, and that over time the tidal forces (as stated by that person) have halted the revolution/spin of the moon.
- that complicates things, so I'm attacking from a different angle, if you will.

The link I gave has a write up, APOD site, that, yes, I have Assumed to be giving good information; has stated something that leads me to believe the far side of the moon has more mass.
- here enters the bucket test, and my reference to a centrifuge.
 
  • #25
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Correction:
The moon's rotation, for those that believe there is one for every orbit, has to be perfectly perpendicular to it's orbital path; and not parallel to the earth's poles. ( I knew something sounded wrong when I wrote it. )
Upon further thought, 2 things must be true:
- at any instant
- if/when the moon rotates

Axis of rotation perpendicular to it's orbital path, and
parallel to the earth's axis of rotation, (the 2 planes that is, and not necessarily alligned.)
 

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