25-03-2002 02:49									#1
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I rose from the seat of ease the other day, and noticed how I no longer feel that I am winning the battle against gravity. Sure, I've put on some weight, perhaps 20 lbs over, but in my heart I know that it is my age that is telling.

Anyway, it got me thinking about gravity, that funny, unaccountable force.

As I looked down at the tile bathroom floor, towards the center of the earth itself, I considered... Where was the force eminating from that has begun to give me such a fight? Well, from everywhere in which there was anything according to science. The very tile itself was pulling at me...a little, and I at it, small consolation. In fact I am pulling at the earth, at the planets, at the sun and all the universe. I am pulling on everything, though the force is feeble, and the farther away the weaker it gets. Still, when you consider the amount of matter in the universe, to exert any pull at all on every bit of it must require a tremendous force, exerted over fantastic distances, yes?

My point is, how can my body, or that tile or any bit of matter continueously exert force without expending fuel of some kind? This whole galaxy is spinning because gravity is constantly pulling. If gravity were to run out of energy then the galaxy would fly apart. Yet even the smallest speck of sand never ever stops pulling for all eternity.

I mean, wtf?

	25-03-2002 03:05									#2
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force is only exerted if there is a body which is away from the body that exerts gravitation. that's newton's explanation.

modern physics says that mass actually makes the time-space continuum around it curve so it is attracted to the center of gravity.


or am I wrong?

	25-03-2002 03:10									#3
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The force does use a sort of "fuel." That fuel would be gravitational potential energy.

quote: I am pulling on everything, though the force is feeble, and the farther away the weaker it gets.

Actually, say, the force between you and the earth is enormous. Only because the earth is so massive does it experience little acceleration from humans.

	25-03-2002 03:13									#4
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It's Lancer thread week again

I've got Europa Universalis now, quite the fun game

As for the topic - gravity works just like electric fields

For both you can use the very simple field model, the only difference would be there is no such thing as negative gravity. And both can only be explained with quantum physics if you want to do it properly. But I'm not there yet

	25-03-2002 03:25									#5
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quote: My point is, how can my body, or that tile or any bit of matter continueously exert force without expending fuel of some kind?

"Fuel" is not expended when a force is exerted. Only if the object moves whilst experiencing a force* is "fuel" expended. Besides the universe is very good at conserveing energy, comets speed up and slow down all the time but "loss of gravity fuel" is not an issue.

*That is a force in the same direction as the motion

	25-03-2002 03:39									#6
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quote: Originally posted by Ecthelion ...there is no such thing as negative gravity.

Never been proven.

	25-03-2002 03:48									#7
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quote: Originally posted by Skanky Burns Never been proven.

If negative gravity existed it could end up powering a perpetual motion machine. Thus it is rejected as a notion by many.

	25-03-2002 04:04									#8
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Consider this: If it wasn't for the electromagnetic force of your individual atoms, the gravitational force would pull you right through the tiles, baby!

Doesn't that make the mind boggle, eh?

	25-03-2002 04:07									#9
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quite a dumb logic.... if it wasn't for electromagnetic force, nothing around us would exist, how does that sound?

	25-03-2002 04:10									#10
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Better than the current hell we live in.

	25-03-2002 04:18									#11
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quote: I am pulling on everything, though the force is feeble, and the farther away the weaker it gets.

Actually, the further away you get from the center of the mass, the more the potential energy increases and the stronger the force. To a certain point, that is.

	25-03-2002 04:22									#12
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quote: Originally posted by Juggernaut Actually, the further away you get from the center of the mass, the more the potential energy increases and the stronger the force. To a certain point, that is.

That point would be the surface of the body under consideration. Above the surface, the force decreases. Sure the GPE increases, but what's that got to do with the price of bananas?

	25-03-2002 04:25									#13
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How do you figure that one out, or are you refering to Gaussian shapes?

	25-03-2002 04:25									#14
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SD - who does that refer to?

	25-03-2002 04:27									#15
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Gravity sucks!

	25-03-2002 04:30									#16
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quote: Originally posted by Chowlett SD - who does that refer to?

Juggernaut.

A result of having several windows open means I missed your post.

	25-03-2002 04:33									#17
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he just thought higher potential energy means more force, what balls

	25-03-2002 04:39									#18
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A force itself doesn't need any fuel. If you tighten a rope between two rods, the rope exerts a constant force without any refuelling. Fuel is energy, not force. When you move something against a force, you spend energy.
This is partly why physicists rarely think in terms of a force. Energy seems to be more abstract at first but its a much easier concept. Force is not wrong, but simply more complicated. Also mathematically.
Gravity cannot "run out of energy". The gravitational field exists. You expend or gain energy if you move something in a gravitational field. When the moon comes a bit closer to earth it gains energy from the gravitational field and becomes faster, i. e. its kinetic energy increases. When it moves away from earth it becomes slower. The sum of the kinetic energy and the energy gained from/given to gravitation remains constant. (in this simple picture, that is).

	25-03-2002 04:39									#19
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"It's Lancer thread week again"-Ecthelion

You must admit Ecthelion, it's been a while.

Thanks for are the replies, I'm still trying to figure it all out.

	25-03-2002 04:40									#20
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quote: he just thought higher potential energy means more force, what balls

A greater rate in change of potential (with respect to distance) would.

	25-03-2002 04:45									#21
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quote: Originally posted by chegitz guevara Gravity sucks!

The Earth has no gravity it sucks

	25-03-2002 04:47									#22
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What is a 'graviton'? A fanciful invention of the writers of Star Trek? Anyone?

	25-03-2002 04:51									#23
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quote: How do you figure that one out, or are you refering to Gaussian shapes?

Yep, Gauss' law works.

Flux(F/m) = [rho]/some constant (whatever the gravitational analogue to the permitivity constant is)
F = GMmr/||r||^3
And M = [rho]4[pi]||r||^3/3

So F = 4/3*G[rho][pi]mr

	25-03-2002 04:54									#24
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*head explodes after only looking at Ramo's post*

quote: Originally posted by Lancer What is a 'graviton'? A fanciful invention of the writers of Star Trek? Anyone?

it's a gravity quantum

	25-03-2002 04:55									#25
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The graviton is the supposed (we don't know if it exists, hell we don't know if gravity can be renormalizable QFT) force carrier for gravity.

	25-03-2002 04:58									#26
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Oh don't turn this all mathematical. It isn't pleasant, it doesn't help Lancer one jot and just scares people away.

Stop it now you naughty children

	25-03-2002 04:58									#27
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A graviton is a concept among those physicists who try to unify the General Relativity with Quantum Theory (which still are not entirely compatible). For SMAC fans: It's "Unified Field Theory".
The basic idea is that if for the electromagnetic field there is the photon as exchange particle, i. e. which communicates the interaction between electromagnetically charged particles, the Weak Interaction has W- and Z- Bosons and the Strong Interaction, which binds quarks in the nucleus of an atom, has the gluons, there should be a similar particle for gravity. There are no experimental proofs for their existence, but some experiments are planned which *might* find them ...
So, at the moment I would regard gravitons as a well-founded speculation.
Not invented by Star Trek

	25-03-2002 05:04									#28
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A simple 'we don't know' would have sufficed.

	25-03-2002 05:05									#29
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Gravity...

I've always wondered - does Archimedes Principle still hold true in space? If so, couldn't the bouyant force it generates offset the effects which the absence of gravity causes in astronauts?

This is all theoretical of course, because unless it filled completely a sealed container it would float around the place. But still, could any of the physicists out there tell me how this law behaves in the absence of gravity?