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What is gravity ?

Posted by: Rolf Guthmann - Fri Dec 02, 2005 7:57 pm
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What is gravity ? 
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Post    Posted on: Fri Jan 13, 2006 12:07 am
Well SuperShuki, I find your chicken scratches pretty hard to read. Since I already know what I think, I will limit myself to commenting on the one about your thinking. You drew something like:

M1---->g1---->M2

and

M1<---- g2<----M2

Where I assume g1 and g2 are the forces on gravity acting on M1 and M2.
Have I understood correctly so far?

You also mention a delta Z, which I assume refers to the change in distance between M1 and M2. It is customary to call the distance between the masses R, not Z, and that is what I will do below.

Now g1 and g2 are forces, as in F=GMm/R^2. That is, the force of gravity between two bodies is calculated as the universal gravitational constant, G, multiplied by both masses (I use M and m instead of M1 and M2, where M is the larger mass, planet or whatever, and m is the smaller mass, satellite or whatever), divided by their separation squared. The point here is the force is the SAME on both bodies. If M (or M1) is the Earth and m (or M2) is a satellite, and the force calculates out to 10 pounds, then the Earth pulls on the satellite with a force of 10 pounds and the satellite pulls on the Earth with a force of 10 pounds. Now a 10 pound pull on the giant Earth will cause an acceleration close enough to zero that it can be ignored, but you can consider it if you really like. However the 10 pound force on the satellite will cause a reasonably large acceleration to that satellite that can be easily measured and considered using every day type numbers.

Now, if the distance between them changes, say they get closer, then the force will change, say to 11 pounds. When they are closer together, the Earth pulls on the satellite with a force of 11 pounds and the satellite pulls on the Earth with a force of 11 pounds. In other words, both g1 and g2 change by exactly the same amount if the distance changes.

So I have to disagree when you say that g1 stays the same but g2 changes.


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Post About gravity   Posted on: Fri Jan 13, 2006 1:59 am
campbelp2002 wrote:
Well SuperShuki, I find your chicken scratches pretty hard to read.


Sorry about that. Wanted to save paper. And my mind is a little haphazard.

About G1 and G2= the forces are the same, but the accelerations are different. The added acceleration of G2 is canceled out by delta z, but the
delta Z is the velocity vector of m1 after it's been lowered in orbit. I forgot about the /r2 bit . . . I don't know if it matters, though . . . because . . . All the acceleration of G1 has to do is move the object a little bit, a bit not compensated for, and it'll eventually spiral. The question is, are Both accelerations compensated for?

Finally,
yes, I'm annoying, but the reason I'm annoying is that whatever I'm saying, be it garbage or golden, it shows that you (whoever is being annoyed) doesn't know what their talking about to be able to explain it to me clearly, and concisely. Don't bring up things that are completely irrelevent to the point (Law of Conservation of Energy). No Law in physics is absolute. . . maybe I HAVE seen something that everyone else has overlooked. It's happened before. Right now, I truly don't understand why something can't spiral into the sun. Is it a Law? :roll:

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Post    Posted on: Fri Jan 13, 2006 2:49 am
Shuki, for God's sake, man, you're attempting to overturn about 40 years worth of orbital mechanics research -- all of which proves you wrong. Just stop now, please.

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Post    Posted on: Fri Jan 13, 2006 9:05 am
Quote:
maybe I HAVE seen something that everyone else has overlooked. It's happened before. Right now, I truly don't understand why something can't spiral into the sun. Is it a Law?

Education ?

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Post Re: I'm faaaaaaaaaaaaaaaaaaaaaaaaaaaaalling! Ahhhhhhhhhhhhhh   Posted on: Fri Jan 13, 2006 1:41 pm
SuperShuki wrote:
[Here we seperate. When you force the object lower, the [angular] velocity increases, because it's falling faster!

Think of it like two magnets. The potential energy is different at different distances/altitudes.


{sigh} OK, I might have explained myself more clearly. Yes indeed - look at my post - the orbital velocity for a lower orbit is greater. If you read my post, you'll see it is considered. I made the assumption of constant velocityjust because I thought that was your original assumption. :(

And one more thing: If you ever try to teach me orbital mechanics again, I'll join the Shuki-bashing club in this forum!

The main thing is that lowering the object's orbit simply moves it to a new, lower, stable orbit. It is so because of the higher angular (and linear) velocity. "Falling" is a misleading word there. The object will continue to orbit around the sun, until the point where you've taken away sufficient energy that no stable orbit is possible any more.

I do hope this is absolutely, positively clear now.

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Post Re: About gravity   Posted on: Fri Jan 13, 2006 1:51 pm
(EDITED a couple hours after I first posted it, so you may want to take a second look).

SuperShuki wrote:
my mind is a little haphazard.
No kidding.

SuperShuki wrote:
The added acceleration of G2 is canceled out by delta z
You say that but you don't justify it. I can think of no reason why it should be true. And you don't mention the added acceleration of G1. If the distance changes, then both accelerations, G1 and G2 will change. And they will change by the same proportion. That is, if G2 doubles, then G1 will double too.

SuperShuki wrote:
I forgot about the /r2 bit
Good gawd man, that is the WHOLE ENTIRE POINT about gravity.

SuperShuki wrote:
The question is, are Both accelerations compensated for?
The answer is, no. The long answer is, see my orbital simulations. But I urge you not to get lost in math. If you don't know how the objects will move at an intuitive, non-mathematical level, no amount of math will help.

SuperShuki wrote:
Don't bring up things that are completely irrelevent to the point (Law of Conservation of Energy).
Conservation of energy is not irrelevant at all. Frequently physicists rely on conservation of energy to point out flaws in otherwise good theories. If the theory violates conservation of energy, then the theory definitely is missing something important and you should think harder. An object spiraling into (or away from) the sun definitely violates conservation of energy.


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Post    Posted on: Fri Jan 13, 2006 8:50 pm
No, Shuki, you cannot (de-stabilize an orbit by a single act of heliocentripital accelleration ["pushing it toward the sun" in his own words from a post that was retracted whilst I was composing]). I am not sure what compels you to believe that you can, but that single point seems to be the stumbling block that has you stymied.

It's like your ball on the shelf example... an object in orbit is NOT like a ball on a shelf, it is like a brand-new really fuzzy tennis ball on a staircase which is carpeted in the "hook" side of Velcro. You can push the ball off of the step it is on, but it will just stick on the next one. It only gets to the bottom by a continuous effort of pushing.


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Post    Posted on: Fri Jan 13, 2006 9:12 pm
SawSS1Jun21 wrote:
No, Shuki, you cannot (de-stabilize an orbit by a single act of heliocentripital accelleration ["pushing it toward the sun" in his own words from a post that was retracted whilst I was composing]). I am not sure what compels you to believe that you can, but that single point seems to be the stumbling block that has you stymied.

It's like your ball on the shelf example... an object in orbit is NOT like a ball on a shelf, it is like a brand-new really fuzzy tennis ball on a staircase which is carpeted in the "hook" side of Velcro. You can push the ball off of the step it is on, but it will just stick on the next one. It only gets to the bottom by a continuous effort of pushing.


So the heavier the ball, the hookier the velcro. More like a tennis ball on a ramp. Why didn't you say so in the begginning? Now I get it! :D :D :D

Only a problem remains . . . :?

Stick a fuzzball on velcro, and eventually, the force of gravity will bend the hook, and the fuzzball will keep on moving.

My problem is that there is a continual force acting on the tennis ball- gravity.

That must be why you compare it to stairs, not a ramp. It's more like sinking stairs. And the hook is orbital velocity. Which still leaves the question . . . Can the hook stop forward movement completely?

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Post    Posted on: Fri Jan 13, 2006 9:44 pm
It is true that gravity works by sucking objects in, providing your continuous force. However most objects are horrified of the idea of being sucked in by large uncouth bodies. This idea is so repellent to them that they stay in a nice stable orbit, far from the awful sucking.

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Post    Posted on: Fri Jan 13, 2006 10:26 pm
I think the best way to understand this stuff is the funnel model. You may have seen these at science museums. There is one in the Austin children's museum and I have seen them in shopping malls, where you roll a coin down the funnel (it is like a wishing well that way, attracting you to throw money in it.) There used to be one at the mathematica exhibit at the Los Angeles museum of science and industry. ( http://www.concentric.net/~Whmsicl/CMSI.html unfortunately that excellent exhibit is gone now, along with the totally awesome model railroad they had. Sigh...) It is a large funnel with a wide shallow rim and gets increasingly steep toward the center. It is designed to simulate the inverse square gravity force. If you roll a ball at just the right speed, it will circle the funnel at one level (it eventually spirals in, but that is due to friction which does not exist in space). Now if you roll it a little too slow, it starts down toward the center, but as it does, it picks up speed which sends it swooping back up to its original starting position. It is simulating an elliptical orbit. This is what happens if you try to push a satellite into a lower orbit. Initially it moves down, but as it does it picks up speed. Eventually it picks up enough speed to arrest it's downward motion and actually start climbing back up to where it was before. If not acted upon by any other pushes (or by friction), it will forever oscillate between a low point and a high point in an elliptical orbit. It won't spiral down.


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Post    Posted on: Sat Jan 14, 2006 7:31 pm
I might point out that if you all simply ignored him, Shuki would eventually have to give up and go away.

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Post    Posted on: Sun Jan 15, 2006 5:15 am
campbelp2002 wrote:
I think the best way to understand this stuff is the funnel model. You may have seen these at science museums. There is one in the Austin children's museum and I have seen them in shopping malls, where you roll a coin down the funnel (it is like a wishing well that way, attracting you to throw money in it.) There used to be one at the mathematica exhibit at the Los Angeles museum of science and industry. ( http://www.concentric.net/~Whmsicl/CMSI.html unfortunately that excellent exhibit is gone now, along with the totally awesome model railroad they had. Sigh...) It is a large funnel with a wide shallow rim and gets increasingly steep toward the center. It is designed to simulate the inverse square gravity force. If you roll a ball at just the right speed, it will circle the funnel at one level (it eventually spirals in, but that is due to friction which does not exist in space). Now if you roll it a little too slow, it starts down toward the center, but as it does, it picks up speed which sends it swooping back up to its original starting position. It is simulating an elliptical orbit. This is what happens if you try to push a satellite into a lower orbit. Initially it moves down, but as it does it picks up speed. Eventually it picks up enough speed to arrest it's downward motion and actually start climbing back up to where it was before. If not acted upon by any other pushes (or by friction), it will forever oscillate between a low point and a high point in an elliptical orbit. It won't spiral down.


Yeah, I've seen one at the now defunct museum of flying in Santa Monica. SpaceCowboy- A very nice point. It you don't like the discussion, you don't have to participate. :cry:

OK, Now I got it. If you're talking about acceleration in a straight line towards the sun in relative to a third object, then you do nothing relative to the orbit. But if you instead consider only the object and the sun, and change your vector as you accelerate, in order to keep heading in the straight line, you will be decelerating. Which will knock you out of orbit. Which will make you spiral into the sun. Ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh!

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Post    Posted on: Sun Jan 15, 2006 3:36 pm
If you KEEP accelerating all the time, you can make it spiral into, or away from, the sun. If you accelerate it for some short period of time and then let it go to move thereafter only under the influence of the sun's gravity, then it will move in an elliptical orbit. The ball spirals down the funnel because the force of friction is pushing on it, directly opposite it's direction of motion, which direction is constantly changing, all the way down to the end. So, yes, applying a continuous force that constantly changes direction by just the right amount could cause a spiral. But it is not the gravity of the sun that causes the spiral, it is the constantly changing external force. The Smart 1 space craft spiraled up from the Earth to the Moon under the constant force of it's ion engine. The navigators continuously changed the direction that the ion engine was thrusting to keep the spiral going. And conservation of energy was not violated because the increasing orbital energy came from the ion engine.


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Post Gravity produced by machine in laboratory   Posted on: Sun Mar 26, 2006 1:31 am
Towards a new test of general relativity?

23 March 2006
Scientists funded by the European Space Agency have measured the gravitational equivalent of a magnetic field for the first time in a laboratory. Under certain special conditions the effect is much larger than expected from general relativity and could help physicists to make a significant step towards the long-sought-after quantum theory of gravity.

More details:
http://www.esa.int/SPECIALS/GSP/SEM0L6OVGJE_0.html
or
http://www.physorg.com/news12054.html


I distrust that this patent
http://www.geocities.com/rolfguthmann/P ... atent.html
and this theory
http://www.geocities.com/rolfguthmann/
has some thing to do with that


I thank all for the help

Rolf

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