# source of earth's gravity...

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I learned from my physics class that it is the strong gravity of earth that not only binds us to it but also keeps the moon in orbit... in a similar fashion that the sun by its extremely strong gravity keeps all the rest of the planets (that we know of) in orbit. Ofcourse, centripetal forces are also involved here but what I wanted to know is the energy source for this gravity.. more specifically, the source of energy of earth's gravity. Is it located at the central core of the earth, as some would predict?? what does it look like?? at what rate is the energy being used up (the power, i.e) and, if it goes at this rate, at approx. what point in time will it be totally depleted... as with the case with all region-specific energies??

Also, I have another question... also somewhat related. It is said that two masses always possess a force field between each other... and the larger the masses... the more stronger is the force firled, and more stronger the attration. I dont remeber the equation for this but its something like F = Gm1m2/4*pi*e0*r^2 (this is entirely from memory, so am not sure if its right).... e0 = absolon zero and r = radius, or more practically, the distance between the two objects m1 and m2 and G is some gravitational constant value that i dont remember at the moment. The main point of the equation is that the attract force between two masses is directly propertional to the size of the masses and inversely prop. to the square of their distance. So my question is... if this is true, howcome the bigger planets like jupiter and saturn are much more distant from our huge sun than the smaller planets like mercury and earth... which are much smaller in comparison?? shouldn't the attractive force make them more closer to the sun than the other small planets?? or is the effect compensated by the large distance between them?? Thanks and apologies for the long-winded post!

-mak10

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Gravity doesn't have an "energy source." Gravity is a force, the Earth's gravity will never be depleted.

The equation you wrote above should be Gm1m2/r^2, and G is 6.7*10^-11 Nm^2/kg^2.

I know this doesn't answer your questions but it's the best I can do right now; maybe you should ask your physics teacher/professor

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Each planet is held in orbit around the sun by a variety of factors including speed, mass and distance from the sun all balanced to keep the planet on its course. It's not purely governed by the gravitational force acting on the bodies in question.

For example, the space shuttle when in orbit does not go up and down to increase and decrease its distance from the planet, it slows down and speeds up. The faster it goes the higher the orbit until such a speed is reached that it leaves orbit entirely.

I'm not really qualified to comment quantitatively on this so I'll leave that for someone else but IIRC the attractive force of gravity is in oppostion to the centripetal acceleration (or is that angular momentum) acting on the body as a result of its velocity.

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muad'dib, you're right that the current theories say nothing about gravity having an energy source, but the fact is that the current theories dont tell us much about gravity at all. So your answer is correct, for now, but is insubstantial theory and shouldn't be stated as fact

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Gravity doesn't have an "energy source." Gravity is a force, the Earth's gravity will never be depleted.

interesting... but what is the source of this force?? And don't you require a tremendous amount of energy to provide the force necessary to bind us to earth and keep the moon, which is thousands of kms away, in orbit?? Anything that exerts a force must obtain energy from somewhere to do so.... it can't out of thin air. I wish I could ask my physics teacher about this but our periods are extremely limited and she doesnt give the full blown explanation that I need, so something remains lingered to my mind, that I spew in here . And she was explaning about something called gravitons that I ahvent the slightest clue of but it didnt answer my question though.

-mak10

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Einstein proposed that space and time are really one (space-time). An object like the sun distorts space-time by sitting in it like a bowling ball on a water bed.

Newton's first law of motion states something along the lines of "an object will move in a straight line at a constant speed unless it interacts with another object."

If we were to roll a tennis ball past the bowling ball sitting on the water bed mentioned above the path of the tennis ball will be distorted. The bowling ball causes a depression in the bed and the tennis ball will roll towards it. If the bowling ball wasn't there then the tennis ball would have continued to move in a straight line.

This is the case with the sun and the Earth; the earth circles around the sun because of the distortion in space-time caused by the sun. The energy required is mass, because mass and energy are the same thing (Eistein proposed this too in his theory of General Relativity I believe). The more mass the sun has the greater the distortion in space-time and the greater the distortion in the path the earth takes around the sun. Instead of a bowling ball sitting on a water bed imagine a ball twice a big in volume made of steel. This will cause a greater depression in the bed and a greater change in the path of the tennis ball.

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This is the case with the sun and the Earth; the earth circles around the sun because of the distortion in space-time caused by the sun. The energy required is mass, because mass and energy are the same thing (Eistein proposed this too in his theory of General Relativity I believe).

Does this also mean the gravitational force exerted by the earth on us and the moon is also caused by this distortion of space-time as a result of the relatively bigger mass of the earth??

-mak10

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muad'dib , it's important to remember the "bowling ball on a mattress" to explain space-time is a way it's used to explain it in 3D terms because it's the only way we can understand it, the only way he could understand it as well obviously as we exist in a 3D environment (4 if time is counted). It would be able to be explained more accurately if it were possible for us to imagine the actual dimensions involved

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...what I wanted to know is the energy source for this gravity.. more specifically' date=' the source of energy of earth's gravity. Is it located at the central core of the earth, as some would predict?? what does it look like?? at what rate is the energy being used up (the power, i.e) and, if it goes at this rate, at approx. what point in time will it be totally depleted... as with the case with all region-specific energies??

[/quote']

The energy isn't being "used up" - energy is conserved. The source of the force is theorized to be graviton exchange.

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I'm not really qualified to comment quantitatively on this so I'll leave that for someone else but IIRC the attractive force of gravity is in oppostion to the centripetal acceleration (or is that angular momentum) acting on the body as a result of its velocity.

The cetripetal force is any force that acts on a body to make it move in uniform circular motion. It can be e.g. gravity, tension in a string or a magnetic force that does this.

"centripetal" = "center-seeking"

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interesting... but what is the source of this force?? And don't you require a tremendous amount of energy to provide the force necessary to bind us to earth and keep the moon, which is thousands of kms away, in orbit?? Anything that exerts a force must obtain energy from somewhere to do so.... it can't out of thin air.

To make a bound system you have to get rid of energy - it doesn't take energy. To remove the moon from orbit would require energy input. If it were to somehow crash into the earth, energy would be released.

To maintain an orbit requires no energy. The work done on an object moving in a circle is zero.

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to my knowledge, conventional theories don't explain in detail how gravity and even magnetism works, i've asked some qualified people about this also. Apart from other theories, like http://www.thefinaltheory.com (a good read, by the way) are there any explanations so far that are applicable to our existing theories?

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To make a bound system you have to get rid of energy - it doesn't take energy. To remove the moon from orbit would require energy input. If it were to somehow crash into the earth' date=' energy would be released.

To maintain an orbit requires no energy. The work done on an object moving in a circle is zero.[/quote']

You do require an initial input of energy from somewhere in order to get rid of it. I want to know 'where' is that "somewhere" and the relevant details of it. No work is being done on the moon, since its motion is perpedicular to the gravitational force of the earth... that I understand, but there is definitely some work done by that 'somwhere' on earth in creating the centripetal force required to maintain the orbit... and thats what I am interested in. For instance, on a smaller scale... if you spin a weight tied to a rope, there is a centripetal force acting tangentially on the object and so the work done by the force on the object is zero... but what of the spinner?? He/she must have had used some energy to create that centripetal force, right?? So the earth, must possess some sort of energy source to create the centripetal force... and thats what I wanna know about. Thanks!

-mak10

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What you say make sense.

However, from what I know, work is done on the moon by the earth unless the moon is not moving in constant orbit round the Earth unless there is a change in gravitational potential, that is moving further away or nearer the Earth. But since it is at the same radius (i.e equipotential), no work is done on the moon by the Earth.

Work = (Final Gravitational Potential - Initial gravitational potential) * Mass of moon

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That book is truely amazing. How could anyone possibly get that published!??

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swansont, I'm not freaking kidding. It really is a good read.

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swansont, I'm not freaking kidding. It really is a good read.

If you mean that in the "preposterously funny" sense, then, OK. Kind of like cult films. "Plan 9 from Outer Space is an enjoyable movie" and all that. But the reliable information content of that site is pretty close to zero.

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Yes' date=' we do understand pretty well how gravity works, just not in special cases (very small distances and very high energies). And we understand how magnetism works extremely well - amazingly so that there has never ever been an experimental observation of magnetism which we cannot explain with the theory.

The website you quote (as Swantson points out) is written by an utter moron. This guy knows nothing about science, and the descriptions of 'science mistakes' are so bad I was getting embarressed reading them. Avoid at all costs.[/quote']

What you mean is we can observe their effects and make predictions as to the outcome of certain experiments.But we dont even know what they are,or how they work,what energy source they draw upon.As for calling the author Mark McCutcheon a moron who knows nothing of science,get a reality check!! Your a 'nobody' on an insignificant forum,you have obviously shown to people here that your knowledge on any science topic is fundamentally average,and thats being complimentary.Yet you think by merely spouting Utter crap that you carry some kind of aura.This person who has shown he understands physics far in advance than you,can get his work published and make significant amounts of money.And you think your words to the contrary are important....a word of advice GET A LIFE.

And if you think thats trolling,or flaming...please dont reply because i dont want you too,Im just pointing out facts.Compared to him your nappy rash...

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Mark McCutcheon has shown he can sell books by appealing to the scientifically illiterate and apathetic, not by displaying a good understanding of physics.

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yes that's what i was getting at, notice I never made any hints at whether that website or book is valid or not.

I often say things like these more to see what the response will be than to actually make a point. A good thing to remember when reading my posts is that I say what I mean, nothing more and nothing less.

It's a good way to get to know people.

However, moments like these make it useless because I don't like being thought of as stupid or a leftist conspirator etc so it often doesn't work

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coming back to the subject... does gravity possess some sort of energy source? it must, according to the fundamental laws of work and energy.... to create the centripetal force, even if the work done by the force tangentially on objects is zero. The idea of gravitons is just as hypothetical as tachyons... neither of them have experimental evidence, although gravitons are predicted by the string theory, which, itself, is in dire need for experimental evidence. But even if we assume gravitons to exist, I don't see how their existence compensates the need for an energy source. Gravitons are simply thought to transmit the attractive force of gravity, not act as a substitute for an energy source that creates the force. just my thoughts...

-mak10

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That's what, to my knowledge, our current theories don't specify.

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