Gravity: What Is It?

rynner2

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Let's keep it simple: gravitational energy is NOT infinite. If a body falls from infinity to Earth, it accelerates all the time until impact. It then has a particular speed (NOT infinite) which is a measure of its energy.

Conversely, if a body on the surface of the Earth is accelerated to this velocity, it will have sufficient energy to escape Earth's gravity and travel infinitely far into space - thus this speed is called Escape Velocity.

(Escape Velocity depends on the mass and radius of the gravitating body - it's proportional to the square root of mass divided by radius.)
 

Dennis_De_Bacle

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I think what Rigmarole is trying to ask is, will gravity 'run out' one day? With the 'dropping an object until it hits' example, the object doesn't simply float away, as gravity is still acting on it. Rigmarole is asking will one day all the objects on the Earth (or indeed anywhere) simply float away, will gravity ever 'fail'?
 

rynner2

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Is that what he was asking? It sounded to me like he wanted a perpetual motion machine! :p
 
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Anonymous

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Well, sorta.

I'm not really asking if gravity will 'run out', because I know it won't. It's been running strong for a good few billion years ;)

I had just never thought about it before, but gravity is it's own energy source. Think about it this way:

We have a wormhole that opens whenever an obejct gets near it. It is in a stationary position above a stationary planet. The "enter" end of the wormhole is nearer to the surface, with the "exit" being directly above it, liek this:

EXIT---------ENTRANCE----------PLANET
----PULL OF GRAVITY------>

Now, if we place an object between EXIT and ENTRANCE, and let go, it will accelerate towards the planet. When it hits the ENTRANCE, it will pop out at the EXIT and continue to accelerate ad nauseum.

If you think about it, we've just created a perpetual motion machine, sort of. It'll accelerate slowly until (I assume) it gets near c, and then all sorts of wacky reltivistic factors would take effect. Of course, it only works in this one small area of space, so there's no real way to harness it, and it assumes that the wormhole has neither gravity nor requires energy to open it.

EDIT: I'll try to clear this all up. I had just come to the realization that gravity doesn't have an energy source outside of itself.
A lightbulbs energy coems form electricity.
A baseball's energy comes from my muscles.
A cars energy comes from gasoline.
Gravity's energy comes from gravity.

I guess that's what happens when you're one of the fundamental forces :p
 
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Anonymous

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rigmarole said:
EDIT: I'll try to clear this all up. I had just come to the realization that gravity doesn't have an energy source outside of itself.
A lightbulbs energy coems form electricity.
A baseball's energy comes from my muscles.
A cars energy comes from gasoline.
Gravity's energy comes from gravity.
Imagine a piece of elastic. Pin one end down and attach the other end to a ball. If you pull on the ball, so that the elastic is stretched, then you will increase the potential energy of the system. If you then let go of the ball it will accelerate and gain kinetic energy. By your analogy above, the energy of the elastic (the analogue of gravity), comes from the elastic itself. :)

Whilst this almost works, it is perhaps best to think of the energy as coming from whatever it was that pulled the ball away from the fixed point. The elastic only acted as a store of energy. In the case of gravity, the energy was put into the system by whatever separated the gravitating masses. The gravitational energy only stores what has been put into it by external forces. :)
 
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Anonymous

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IIRC

any mass bends space time
as a result gravity occurs
the energy involved is a result of this process
to imply that gravity may end is to sugest that time or space may end so.....................
 
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Anonymous

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Fortis said:
Imagine a piece of elastic. Pin one end down and attach the other end to a ball. If you pull on the ball, so that the elastic is stretched, then you will increase the potential energy of the system. If you then let go of the ball it will accelerate and gain kinetic energy. By your analogy above, the energy of the elastic (the analogue of gravity), comes from the elastic itself. :)

Whilst this almost works, it is perhaps best to think of the energy as coming from whatever it was that pulled the ball away from the fixed point. The elastic only acted as a store of energy. In the case of gravity, the energy was put into the system by whatever separated the gravitating masses. The gravitational energy only stores what has been put into it by external forces. :)
But in that analogy, it's clear that the energy from the elastic comes from me stretchig it. It's not so clear where the energy from gravity comes from.

We seem to have a problem. Half of the people are saying that gravity is a wrinkle in space-time that causes things to 'fall' toward them. This makes sense, if you imagine that things are always travelling in a straight line, and gravity just makes 'straight' a different direction.

However, stating that gravity si a field still does not answer the question as to where gravity's energy comes from. I'm not understanding, how does gravity store what has been put into it?
All things with mass ahve gravity. If a planet jsut popped into existence, it would have gravity, even though no object or force had never acted upon it before.

any mass bends space time
as a result gravity occurs
the energy involved is a result of this process
to imply that gravity may end is to sugest that time or space may end so.....................
Which I didn't (or didn't mean to.)
 
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Anonymous

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Mass and Gravity and a Question About Black Holes

rigmarole said:
However, stating that gravity si a field still does not answer the question as to where gravity's energy comes from. I'm not understanding, how does gravity store what has been put into it?
All things with mass ahve gravity. If a planet jsut popped into existence, it would have gravity, even though no object or force had never acted upon it before.
Gravity is a property of Mass.

Mass is very much a folding of space/time/energy.

Whether, in some aspect of our extended, 4+ dimensional, reality, gravity has it's own particle, or even that it has a wavelike place on the electromagnetic spectrum, is the stuff of conjecture.

'Does matter eventually unscrumple, give up its energy and evaporate?' is one of the big physics questions of modern times. Do even Protons have a half life?

If mass evaporated, once again into its original energies, gravity would also vanish.
_______________

What I'd like to know is, since a 'Black Hole' is a singular point of infinite mass and gravity, what does it do to the space it has to pass through on its path throught the Universe?

Indeed how does it travel through space with out collapsing the rubber sheet form in completely?

Is that how 'Wormholes' are actually formed?
 
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Anonymous

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Re: Mass and Gravity and a Question About Black Holes

AndroMan said:
Gravity is a property of Mass.

Mass is very much a folding of space/time/energy.

Whether, in some aspect of our extended, 4+ dimensional, reality, gravity has it's own particle, or even that it has a wavelike place on the electromagnetic spectrum, is the stuff of conjecture.

'Does matter eventually unscrumple, give up its energy and evaporate?' is one of the big physics questions of modern times. Do even Protons have a half life?

If mass evaporated, once again into its original energies, gravity would also vanish.
Well, no ones really addressing my question, so I guess I'll just give it up :p
_______________

What I'd like to know is, since a 'Black Hole' is a singular point of infinite mass and gravity, what does it do to the space it has to pass through on its path throught the Universe?

Indeed how does it travel through space with out collapsing the rubber sheet form in completely?

Is that how 'Wormholes' are actually formed?
Well, I think the whoel problem is in the analogy. We use the rubber sheet/balloon analogy to explain gravity. However, empty space is just that. Gravity is a flexure in the plane of existence, which is nothingness containing somethingness. Any anlogy we sue to try to explain somethign like this is going to be flawed, wicne we're using an object to try to understand the concept of nothingness. I don't think our brains can really comprehend the ideas of nothingness, and the opposite, infinite. Which sucks, becasue the universe is both, an infinite expanse of nothing.



:eek!!!!:

:p
 
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Anonymous

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Re: Re: Mass and Gravity and a Question About Black Holes

rigmarole said:
However, empty space is just that. Gravity is a flexure in the plane of existence, which is nothingness containing somethingness.
Except 'empty space' isn't really empty. It's inflated.

Complimentary matter and anti-matter particles are forming and annhilating each other all the time (every 10 to the -32 times per second) and weird anti-forces are at work, keeping our reality inflated.

Gravity and mass seem to obey strict rules, which break down only when a mass collapses in on itself to form a blackhole, effectively punching a hole in reality and space/time.

A falling object would only approach infinite speed falling into an infinite mass, which would exhibit infinte gravitational attraction.

And since the constant for the speed of light is more, or less fixed, then you could expect the mass to:

a. freeze relative to time and become a permanent fixture on the 'Event Horizon' of the Blackhole,

b. Cease to exist as matter and give up its energy, obeying the Einsteinian formula, E=MC²

Is Gravity's energy infinite? No, It's energies are a function of the inflated, multi-dimensional, rubber sheet of space/time distorted by mass.

You may be getting confused, by the 'athlete and the tortoise' nature of gravity, as it falls off in inverse proportion to the distance between the masses?
 
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Anonymous

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Plus, you may be factoring in a high intial acceleration of the original 'falling' object, which did not originate under gravitational influence?
 
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Anonymous

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Boring science fact: protons do decay, but very slowly with a half life of approximately 10^32 years.

Equivalent to one decay a year in an Olympic sized swimming pool.

And yes people do try to measure this.

And yes it may be the dullest job on the planet.

I now return you to your thread.
 

Bilderberger

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rigmarole - it does appear that no one is addressing your question.

If I understand correctly - you are saying that, if the earth was surrounded by an enormous (I hesitate to say infinite because of the complications that would cause) number of small objects - gravity would pull those objects towards the earth and therefore experience kinetic energy.

So, as the amount of kinetic energy is only limited by the number of objects available to fall within the gravitational field - the relationship between energy and gravity does not comply with our normal understanding (i.e. energy is either converted from other energy or from the destruction of mass).

I am intrigued by this as well - and can certainly offer no reasonable answer.................but I thought that you may find it reassuring that someone has actually understood your query rather than just replying with explanations of what gravity/space/time etc are...............
 
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Anonymous

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I would like to point out that I have explained where the energy in gravity comes from; did my answer seem like new age twaddle?
For that I apologise- it is in fact the currently accepted cosmological explanation - if you did not understand it I can make it simpler (but not much)...
 
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Anonymous

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Bilderberger said:
rigmarole - it does appear that no one is addressing your question.

If I understand correctly - you are saying that, if the earth was surrounded by an enormous (I hesitate to say infinite because of the complications that would cause) number of small objects - gravity would pull those objects towards the earth and therefore experience kinetic energy.

So, as the amount of kinetic energy is only limited by the number of objects available to fall within the gravitational field - the relationship between energy and gravity does not comply with our normal understanding (i.e. energy is either converted from other energy or from the destruction of mass).

I am intrigued by this as well - and can certainly offer no reasonable answer.................but I thought that you may find it reassuring that someone has actually understood your query rather than just replying with explanations of what gravity/space/time etc are...............
Exactly.

Let's say I throw a baseball in a vacuum. It will only have as much energy as I put in to it. No more, no less. However, every time I throw a baseball from that vaccuum at a planet, the baseball gains energy from gravity acting on it, and will continue to gain energy until it reaches terminal velocity or hits the ground.

I'll use my wormhole analogy

EXIT-----------ENTRANCE

I throw a baseball towards ENTRANCE, between EXIT and ENTRANCE. It will have a certain energy value (let's just say 5 units). When it enters the wormhole, and comes out the other end, it will always only have 5 energy units, assuming the wormhole is massless and gravity-less.

EXIT---------ENTRANCE-----------PLANET
-------PULL OF GRAVITY---->
Now let's say I throw the baseball between EXIT and ENTRANCE. It begins with 5 units, but let's say that gravity accelerates at 1 unit/sec (Horribly off, but just for the example). It will continue to accelerate between EXIT and ENTRANCE< getting faster and faster each time it passes through. Now, unless someone can explain it to me otherwise, the baseball will forever continue to gain energy as it approaches c, but will never reach it.

Androman-
I think we're using two different definitions of nothing. I use nothing as a lack of energy or matter, you're using it as a lack of existence (having 3 dimensions means somethign isn't truly empty).
 
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Anonymous

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Wormholes are mathematical solutions to certain space time questions; if you want to try to get infinite energy out of them you will find that they observe the conservation of energy, just as everything else in the universe does.

In this case the wormhole would experience an aceleration toward the planet; if you wanted to keep it stationary while your falling object accelerated toward the speed of light you would need to expend the same amount of energy to hold the wormhole in position as it would to accelerate the object to that speed under normal conditions.
 
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Anonymous

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Eburacum45 said:
Wormholes are mathematical solutions to certain space time questions; if you want to try to get infinite energy out of them you will find that they observe the conservation of energy, just as everything else in the universe does.

In this case the wormhole would experience an aceleration toward the planet; if you wanted to keep it stationary while your falling object accelerated toward the speed of light you would need to expend the same amount of energy to hold the wormhole in position as it would to accelerate the object to that speed under normal conditions.
Well, the wormhole was just a gimmick. I was using it under the assumption that it was massless and gravity-less (not a true wormhoel and probably impossible, but I was using it to point out what I don't understand abotu gravity, not a discussion fo wormholes.)

However, I do understand what you mean. The universe just makes sure that it's impossible to use gravity to do what I describe. For some reason, the more I learn about the universe, the more it seems to be taking an active role as opposed to a passive one. Maybe it's just the way it's described, how certain laws of physics "make sure" the impossible don't happen. Kinda denotes an invisible hand at work.

Or maybe I'm just nuts :p
 
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Anonymous

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rigmarole said:
However, the two objects do not impart gravity onto eachother.
But, they do.

Sling shot one object round the gravity well of another and one object picks up energy, but the other object loses it in the form of loss of momentum.

If the sling shotted object is a baseball, or an artificial satellite, and the sling is a planet the size of Earth, then all well and good. But if the slingshotted object was something the size of the moon, then expect terrible consequences.

Although the Moon is perpetually falling throught the Earth's gravitational field, its gravitational field is influencing the Earth and the tides. Both objects are slowly losing momentum and may eventually crash into each other.

...

Crash an object into the surface of the planet, expect a crater, small object, small crater, big object big crater. Energy is given up as an explosive force. The planet gains the mass of the fallen object and the gravitational pull also increases. Do it enough, get a star.

Newton and Einstein worked all this out and I don't think gravity is disobeying any rules here.
 
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Anonymous

Guest
its gravitational field is influencing the Earth and the tid

why should the moon infuece tides
if its gravity is strong enough to move large bodys of water why isnt it undermining a dams foundatons in fact any building would have such a problem if they were being constantly flexed and sutably large enough.

and secondly if its gravitational pull is so strong how did the lem moon lander seem to free itself from its pull without what seem like not too much of a strugle.weve all seen the amount of enegy needed to escape our gravity

and thirdly if is infuencing our planet ,the moon is having the same sort of stress as we recive from it.
so why is it labled as dead with no gelogical activity?
surely something must be going on inside it after all this time surely?
 

rynner2

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Re: Re: Gravity, energy

AndroMan said:
Although the Moon is perpetually falling throught the Earth's gravitational field, its gravitational field is influencing the Earth and the tides. Both objects are slowly losing momentum and may eventually crash into each other.
No, Momentum is conserved. In fact, the tidal interaction is transferring momentum from the rotating Earth to the Moon, which means the Moon's orbit is slowy getting larger, as the Earth's spin decreases.

This process will continue until the 'day' and the 'month' are equal, which means that one side of the Earth will be permanently turned towards the moon. The new 'day' would be about 40 times longer than the present one, IIRC.


Tinfinger. yes the Moon's gravity is very weak, but it does control the tides. You need to do the maths to fully understand how this works, and here is not the place to explain it. (Believe me, I've spent hours on it, preparing talks!) A web search on Moon, tides, gravity, will no doubt turn up pages af varying compexity, if you really want to look into it.

And yes, the moon does flex under Earth tidal's forces, but whether this is sufficient to produce volcanic activity is unproven (although there are reports of Transient Lunar Phenomena).
 
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Anonymous

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Re: Re: Re: Gravity, energy

rynner said:
No, Momentum is conserved. In fact, the tidal interaction is transferring momentum from the rotating Earth to the Moon, which means the Moon's orbit is slowy getting larger, as the Earth's spin decreases.
Thanks, Rynner! :)

I knew conservation of momentum came in somewhere!
 
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Anonymous

Guest
After a bit of practice, I've found a way to explain gravity a little more clearly;
expansion and gravity are inextricably entwined, and every cosmologist is well aware of that fact;
two or more massive bodies in our universe have a potential energy due to gravity when separated from each other.

This potential energy is supplied by the expansion of the universe since the big bang.

If you took the energy involved in the Big Bang and the expansion of the universe, and balanced it against the gravity of all the mass and energy in the universe, it would equal zero (except in brane theory, where the energy is balanced out over several branes).

The Universe came from nothing, and in total it adds up to nothing, like a pair of virtual particles on a huge scale.
 
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Anonymous

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Eburacum45 said:
After a bit of practice, I've found a way to explain gravity a little more clearly;
expansion and gravity are inextricably entwined, and every cosmologist is well aware of that fact;
two or more massive bodies in our universe have a potential energy due to gravity when separated from each other.

This potential energy is supplied by the expansion of the universe since the big bang.

If you took the energy involved in the Big Bang and the expansion of the universe, and balanced it against the gravity of all the mass and energy in the universe, it would equal zero (except in brane theory, where the energy is balanced out over several branes).

The Universe came from nothing, and in total it adds up to nothing, like a pair of virtual particles on a huge scale.
Alright, I understand now, it all balances out. My entire problem was I thought it didn't. Thanks :)

Of course, the assumption that is balances out is based on the idea that CoE is in effect on a universe-wide scale, not the other way around ;)

And I wouldn't be too sure that the universe came from nothing. I hear Stephen Hawkings is planning on screwing with our brains more in a couple months :p
 
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Anonymous

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rigmarole said:
And I wouldn't be too sure that the universe came from nothing. I hear Stephen Hawkings is planning on screwing with our brains more in a couple months :p
I wonder if that's anything to do with the bit at the end of 'A Brief History Of Time,' where he plays about with a few models of the expansion of the Universe? The 'cone' shaped (Big Bang) model, the 'parabola' shaped (Steady State) model, etc? :confused:
 

Bilderberger

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Eburacum45 said:
After a bit of practice, I've found a way to explain gravity a little more clearly;
expansion and gravity are inextricably entwined, and every cosmologist is well aware of that fact;
two or more massive bodies in our universe have a potential energy due to gravity when separated from each other.

This potential energy is supplied by the expansion of the universe since the big bang.

If you took the energy involved in the Big Bang and the expansion of the universe, and balanced it against the gravity of all the mass and energy in the universe, it would equal zero (except in brane theory, where the energy is balanced out over several branes).

The Universe came from nothing, and in total it adds up to nothing, like a pair of virtual particles on a huge scale.
Aha - I see - that makes sense. I guess the problem for the layman is viewing the universe on a, for want of a better term, universal scale................

Like with evolution, it is very hard to mentally comprehend the periods of time involved - as our experience can never come close to grasping the full extent.
 
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Anonymous

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AndroMan said:
I wonder if that's anything to do with the bit at the end of 'A Brief History Of Time,' where he plays about with a few models of the expansion of the Universe? The 'cone' shaped (Big Bang) model, the 'parabola' shaped (Steady State) model, etc? :confused:
Well, there's so many different theories that are so completely opposite of each other that I really don't think we'll be finding out the truth any time soon.

No theory of the universe, even if it is 100% correct, will make any sense. Boil down any theory and it comes down to the universe came from nothing. Which basically contradicts the entire basis of science and understanding. Science is based in the idea that the universe is governed by set laws, and cna be predictable with enough observation. But if the universe itself came about as a random act with no instigation of law about it, then I think our brains are gonna go out the window. We'll keep digging farther and farther back, past the big bang, past Z-particles, past parallel and alternate universe collisions; we'll still be sitting here with the question of what or who lit the fuse to start it all. I don't know if our brains are going to be able to comprehend the answer.

After all, even empty space had to come from somewhere.
 
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Anonymous

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rigmarole said:
Boil down any theory and it comes down to the universe came from nothing. Which basically contradicts the entire basis of science and understanding.
No such thing as a free lunch? Ha! :hmph:
 
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Anonymous

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rigmarole said:
Long as I don't get shafted with the bill...
"Mr Igmarole? Sign here please. Now where do you want it?"

"Want what?"

"Your Universe, what you ordered. The one with the funny laws of gravity. Bit big for this hallway. Where will we put it? Round the back?'

'Do you want to pay now, COD? Or, will you wait for the bill? There's an instalment plan."
 
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