Question about gravity

[JollyRoger]

On Earth when an object is affected by gravity in that it falls to the ground.
In space an object produces gravity depending on the size and density.
When you spin a sphere on an axes on earth everything on the surface of the object is repelled, and the opposite is true in space.

What Produces gravity? why does it exist? How does it work. Why do objects in space attract one another and why is the same not true here on Earth where we are within a gravity field.

 

[Zeuzzz]

What Produces gravity? why does it exist? How does it work. Why do objects in space attract one another and why is the same not true here on Earth where we are within a gravity field.

Gravity is though to be caused exclusively by the attraction of mass. How this attraction occurs is still not known, mainly due to the weakness of gravity compared to other forces which makes experiments testing its exact nature very hard without EM forces interferring with the experiment. Millikan's oil drop experiment is a fine example of this, where you are able to make an drop float by applying an electric field. When this is done the entire mass of the earth is pulling down on the drop, yet an electrical effect can counter it with ease, which shows how hard it is to directly test the mechanism by which gravity works.

Maxwell tried to explain gravity with electromagnetic effects, but with no avail, and it has since been considered to be a completely separate force from EM effects.

It doesn't help that the definition of mass is not very precise, it is explained in term of gravity, and gravity is explained in terms of mass. Wiki says; http://en.wikipedia.org/wiki/Mass

Mass is a fundamental concept in physics, roughly corresponding to the intuitive idea of "how much matter there is in an object".

Hardly definitive to say the least, what exactly 'mass' is, is another question that is quite hard to answer too

 

[steve s]

...and the opposite is true in space.

Not sure I understand that part. Are you talking about creating artificial gravity by rotating a spacecraft? The same principle is at work. But if you're inside the spacecraft, you'll stick to the outer walls.

What Produces gravity? why does it exist? How does it work.

Matter warps the fabric of spacetime. I'm sure you've seen the analogy of a heavy ball on a large sheet of rubber. Try googling "general relativity."

Why do objects in space attract one another and why is the same not true here on Earth where we are within a gravity field.

They do attract each other, but other forces (such as friction) are greater than any attraction due to gravity.

Steve S.

 

[JollyRoger]

Not sure I understand that part. Are you talking about creating artificial gravity by rotating a spacecraft? The same principle is at work. But if you're inside the spacecraft, you'll stick to the outer walls.

I understand sentrifical force for the most part I was wondering the mechanism of Gravity what causes and it?

Matter warps the fabric of space-time. I'm sure you've seen the analogy of a heavy ball on a large sheet of rubber. Try googling "general relativity."

yes I have but how does warping space time produce gravity

They do attract each other, but other forces (such as friction) are greater than any attraction due to gravity.
Steve S.

not sure on this one but how would you have friction between to objects without gravity pulling the objects close enough to each other to produce friction

 

[JollyRoger]

Gravity is though to be caused exclusively by the attraction of mass. How this attraction occurs is still not known,

I often wondered because they always seem to dance around the specific subject of its mechanism

 

[MG1962]

Gravity is a myth

The Earth sucks

 

[bobhope2112]

I understand sentrifical force for the most part I was wondering the mechanism of Gravity what causes and it?

There really is no such thing as a "centrifical"/centrifugal force. Just to be clear what we're talking about: People will describe the tendency for you to fly off of a fast moving merry-go-round as being acted upon by a centrifugal force. The reality is that it's just inertia at work. The merry-go-round is turning away from you, and if there is no force on you to make you turn with it, you'll keep going straight and fall off.

What causes gravity? Excellent question, but one that need not be addressed to have a coherent theory of gravity. As long as the theory describes our observations of gravity, it's of use. If a Grand Unification Theory ever pans out to describe all of nature's forces, en masse, I suspect we'll have a bit more of an answer as to what /causes/ gravity, but it may be too abstract to satisfy your practical sense.

Why do objects in space attract one another and why is the same not true here on Earth where we are within a gravity field.

Objects do attract each other here on Earth. In fact, it's the principal reason you don't go flying off this merry-go-round/planet as it spins. It is a relatively week force, though, so you won't see two billiard balls slamming together, like a couple of magnets, from their gravitational attraction. A subtler interaction comes to mind: If you hold a plumb bob next to a mountain, it will actually deflect a bit instead of pointing "straight down." The mountain's mass attracts the plumb bob, but the far dominant force will be the massive Earth.

 

[Fredrik]

On Earth when an object is affected by gravity in that it falls to the ground.
In space an object produces gravity depending on the size and density.

Gravity works the same on Earth as it does in space.

When you spin a sphere on an axes on earth everything on the surface of the object is repelled, and the opposite is true in space.

Uh, no. Objects move in straight lines unless a force is acting on them. The gravitational attraction between you and the Earth is what's keeping you from moving in a straight line (i.e. from being "thrown" into space).

What Produces gravity? why does it exist? How does it work. Why do objects in space attract one another and why is the same not true here on Earth where we are within a gravity field.

The same is true on Earth. What makes you think it isn't?

No one has a complete answer to the first two questions. There are however two good theories of gravity: Newton's and Einstein's. Einstein's is better in the sense that it agrees with the experimental results to a higher degree.

Newton's theory simply states that the magnitude of the force between two massive point particles with masses m₁ and m₂ a distance r apart, is m₁m₂/r² (in units chosen to simplify the formula), and that the force is attractive.

Einstein's theory is much more difficult to understand. It describes gravity as a geometric effect. Matter tells space how to curve, and space tells matter how to move. It's impossible to really understand Einstein's theory without learning differential geometry.

 

[LordoftheLeftHand]

I often wondered because they always seem to dance around the specific subject of its mechanism

This "mechanism of mass" is an interesting concept, it is sometimes called the Higgs Mechanism. The ATLAS experiment should be going online sometime this year. It is supposed investigate the Higgs Mechanism (which to this date has never been observed). You might be hearing a lot about this in the near future.

Here is a nice video about it:
http://atlasexperiment.org/multimedia/html-nc/feature_atlas.html

LLH

 

[sol invictus]

When you spin a sphere on an axes on earth everything on the surface of the object is repelled, and the opposite is true in space.

As Fredrik already pointed out, that's not true.

What Produces gravity? why does it exist? How does it work.

One answer is that energy curves space (the rubber sheet with a bowling ball on it), and objects just move in straight lines as usual - but on that curved sheet. If you didn't know the sheet was warped, you'd say there must be a force acting to make the object move in a curve, and that's the thing we call the force of gravity.

Another answer is that the force is caused by the exchange of gravitons, which are a hypothetical type of elementary particle. Gravitons are emitted and absorbed continuously by anything with mass/energy, and this happens more often and more gravitons are involved if the object is more massive, which is why the force is stronger.

Why do objects in space attract one another and why is the same not true here on Earth where we are within a gravity field.

The same is true on earth.

 

[robinson]

What Produces gravity?
why does it exist?

Well, we are sure matter produces gravity. Because gravity doesn't exist without matter. Why and how this is so, is one of the greatest mysteries.

 

[sol invictus]

Well, we are sure matter produces gravity. Because gravity doesn't exist without matter. Why and how this is so, is one of the greatest mysteries.

Why do people keep saying this? It's really not any more of a mystery than why electric charge produces an electric field. We have extremely precise theories to describe both. Of course you can always keep asking why why why and come to a point where there's no answer - but you can do that with anything.

I would say gravity is understood better than almost anything else in the world. Certainly we understand it far better than we do prosaic things like wind, the human body, or the mixing of cream as it's added to coffee.

 

[69dodge]

On Earth when an object is affected by gravity in that it falls to the ground.

On Earth, objects fall towards the Earth, because the Earth is massive.

Far from Earth, objects also fall towards any massive body that happens to be nearby.

In space an object produces gravity depending on the size and density.

Yes, and the same occurs on Earth.

When you spin a sphere on an axes on earth everything on the surface of the object is repelled,

Yes.

and the opposite is true in space.

No. Where did you hear that?

What Produces gravity? why does it exist? How does it work.

Those are hard questions.

Why do objects in space attract one another and why is the same not true here on Earth where we are within a gravity field.

But the same is true here on Earth. The gravity field we're in, in fact, is just the Earth attracting other objects.

 

[robinson]

Why do people keep saying this? It's really not any more of a mystery than why electric charge produces an electric field. We have extremely precise theories to describe both.

Describing gravity is easy, and was understood long ago. Describing something is not the same as understanding how, or why. There is no theory for gravity like there is for the other fundamental forces. Saying there is, is dumb.

I would say gravity is understood better than almost anything else in the world.

Again, the question isn't about understanding, it is about explaining.

 

[sol invictus]

Describing gravity is easy, and was understood long ago. Describing something is not the same as understanding how, or why. There is no theory for gravity like there is for the other fundamental forces. Saying there is, is dumb.

Last time I checked we had a perfectly good theory of gravity, just as we do for the other fundamental forces (it's called general relativity). We're not sure how to quantize it, but the uncertainties in calculations due to that are MUCH smaller than uncertainties in calculations involving the other forces (which stem from our ignorance of physics at high energies).

Our theory of gravity is much more precise than any other theory we have, at least in a certain technical sense.

 

[Zeuzzz]

Just for some fun;

Q1 Where is gravity of the Earth the strongest?

A - On the surface of the Earth
B - In the centre of the Earth
C – Somewhere about halfway down to the centre of the Earth


Q2 If you dig yourself about one thousand of miles into the Earth, what happens to gravity?

A. - Increases definitely.
B. - Stays more or less constant.
C. - Decreases definitely.

There is more to it than you might think.

 

[Southwind17]

I would say gravity is understood better than almost anything else in the world. Certainly we understand it far better than we do prosaic things like wind, the human body, or the mixing of cream as it's added to coffee.

Really? Please go ahead and explain it, then, and satisfy the majority of the Earth's collective unfulfilled wonderment!

 

[sol invictus]

Really? Please go ahead and explain it, then, and satisfy the majority of the Earth's collective unfulfilled wonderment!

Einstein already did, nearly a century ago.

I can use his theory to compute the orbits of planets to very high precision (and the accuracy is not limited by the theory, but by uncertainties in the positions of other gravitating bodies). I can compute the scattering of two low-energy gravity waves to a theoretical uncertainty less than for the scattering of two electrons at the same energy.

There is no gravitational experiment I can't predict the result of with precision greater than the experimental error using GR (apart from chaotic systems, but the difficulty there has nothing do with a lack of understanding of the theory of gravity).

 

[Southwind17]

Just for some fun;

Q1 Where is gravity of the Earth the strongest?

A - On the surface of the Earth
B - In the centre of the Earth
C – Somewhere about halfway down to the centre of the Earth


Q2 If you dig yourself about one thousand of miles into the Earth, what happens to gravity?

A. - Increases definitely.
B. - Stays more or less constant.
C. - Decreases definitely.

There is more to it than you might think.

Simplistically:

Q1 - None of those. The effects of gravity would be more apparent on the surface of the Earth.
Q2 - None of those. The effects of gravity would decrease.

 

[Southwind17]

Einstein already did, nearly a century ago.

... and he said what?