The gravity of things

I have some questions I really don't understand concerning gravity.
Now I hope, I will not get flamed for them.

I always wondered if gravity was zero at the center so i went and searched a little. Now I wonder how gravity is zero at the center of mass, but decreases from sea-level up?
From what I understood, the accumulated mass between you and the center is what defines gravity, so it should increase with every molecule you put between you and the center.

What stops the curvature? And how is the moon not more affected by the suns gravity field?

I read some time ago about this weird experiment in mining lifting holes they did in tamarak. Where they hanged two identical plumb lines couple of hundert meters down and apart, then measured the distance between the top and bottom, they expected to calculate the diameter of the earth, but the numbers implied a concave earth.
The distance at the bottom was bigger than at the top.
This has been a headscratcher for a while too. Instead of turning everything thing upside down there could be something along the lines of gravity to explain it. Like a resistance pushing against the acceleration towards the center?
I don't know... it's quite late... I look forward to any contributions in the morning

a reply to: Terpene

link

The Sun's gravity pulls the planets in orbit around it, and some planets pull moons in orbit around them. Even spacecraft are in motion through the solar system, either in orbit around the Earth or Moon, or traveling to further worlds, because of gravitational forces.

a reply to: Terpene

Gravity is a fictitious force.

originally posted by: AlphaBat
a reply to: Terpene

Gravity is a fictitious force.

Where you the guy that asked about acceleration and teh gravity in a past thread today that was shut down?
Created a new account hmmm ?

a reply to: network dude

Isn't that model exactly my problem?

It brings more questions than answers.

The fabric has tension to resist the gravitational pull, where is that force factored in, and what is it?

Does all mass bend the fabric into the same dircetion, which direction is that?

I'd expect gravity to decrease when no more mass was between me and the center.
Obviously the density of the medium between me and the center defines the increment of gravity, but why does it decreased from sea-level up? Is it the curvature of other bodies that start to negate earth curvature, so early on?

If i try to imagine it in 3D, i really get dizzy

a reply to: Terpene

Gravity is zero at the center of mass because it is the center of the mass. The mass is surrounding the center evenly in all directions, assuming a sphere, and thus cancels out the force to zero.

Gravity is highest at the surface because it is where the force is all on one side and in contact with the measuring device. As you get farther from the surface, gravity lessens just as with visible light getting dimmer with distance.

In the Moon and Earth system, the center of mass is not the center of the Earth. It is offset toward the Moon by the mass of the Moon. This causes the tides.

As far as the Sun affecting the Moon more than it does, the Sun affects the center of the mass of the Earth and Moon as a single body and not separately. This is because the Sun is over 400 times farther from the Moon and Earth as the Moon is from Earth.

a reply to: Spacespider

I did read that massacre. So this is the second time today that physics facts have you stumped.

a reply to: beyondknowledge

Thanks, so it is other bodies gravity fields that have a stronger pull than the mass of air and everything from sea level up?
like all the air does not add up to anything and gets negated from sea-level upwards by the sun and moon gravity fields?
i honestly don't know, it sounds too strange, I'm getting something wrong?

a reply to: Terpene
At a local level, such as the plum bob experiment, I believe variations on density can have an effect.

The USGS has gone through the trouble of mapping gravitational anomalies in the US.
mrdata.usgs.gov...

Fixed link

a reply to: Terpene
I'm no physicist so take this all with large grains of salt.

Gravity has a square function as it relates to distance somewhere in the equation I believe. Every molecule between you and the center also moves you away from the center. I don't know the mass calculation where distance is overcome by mass, but air would probably fall far short of that. I would guess the relatively low mass of the very thin atmosphere is negligible compared to the whole planet. In other words the detectable edge of Earth's mass would be fairly irrelevant for tiny measurements like the experiment you mentioned. Effectively sea level is the settled mass of 99.99999% of the mass and, with fluid moving, it's a constantly shifting level but meaningless distinction for small measurements. We also know there are places below sea level that are in fact not full of water, merely air. Maybe somebody knows about people that have tried to measure it more precisely.

The moon is quite far from the sun, like earth, so the action of gravity is quite diminished. Somewhere in that is an equation that relates to the straight forward momentum vs the action of gravity. We're also all moving through space in with our solar system and galaxy, all in varying cohesion with the rest.

As for the experiment I would need to hear how they were measuring and the methods. A couple hundred meters isn't a huge variable and I'd expect the variance would be quite small leading to an increased chance of exceeding the reliable detection limit of whatever tool they used.

a reply to: Terpene.

The density of the air as compared to the rest of the planet can be ignored. Also the air is very very thin wmen compared to the Earth's diameter.

Also, don't think of gravity as fabric. It is much more than that. This might help. Oh, the planets don't actually leave visible trails.



The entire solar system just passed through the galactic equator a few years ago on its orbit around the galaxy.

a reply to: Terpene

A lot of your questions can be answered with an understanding of Newton's Law of Gravitational Force. I ask you to look it up because I don't know how to format that properly in a post.

F is the force of the gravitational attraction. Keep in mind, force is a vector quantity, it has a direction.

G is the Gravitational Constant. We can ignore that for the moment because it is a constant.

M1 x M2 is the product of the masses involved. Note that there are only two here. If you want to talk more than two masses then you have to work out the forces between each pair then combine the vectors to get a net force of gravitational attraction on any particular body in relation to the others.

For instance, If you wanted to figure the net gravitational pull on the Moon caused by the Earth and the Sun, you would have to calculate the pull between the Earth and the Moon, then the Sun and the Moon, and then combine those two vector forces for the net pull.

R is the distance between the centers of the masses. One thing you'll note here is that R can never be zero. mathematically, because dividing by zero is undefined. Physically, because no two objects can occupy the same space.

So, one thing you will notice from the formula, the amount of matter between the two centers has no effect on the gravitational force. Whether you're standing on a mountain at 1000' above sea level or standing in the gondola of a balloon 1000' above sea level, the force is the same.

That being said, celestial bodies are not necessarily homogeneous. For instance, if you had a planet that was mostly lead in the northern hemisphere and mostly aluminum in the southern hemisphere, its center of gravity would be a good distance away from its geographical center.

The formula also disproves the idea that a feather will "fall" as fast as a cannonball in a vacuum. The more massive object will fall faster, but the relatively small difference in mass between a feather and a cannonball would mean that you would need a very accurate timepiece to measure it.

I don't know about the mining experiment you mentioned, but offhand I could see a lot of room for error. How far apart were the holes? How did they measure the distance between the plumbs? Were the plumbs made of ferrous metals or alloys? How could they eliminate any pendulum motion? Lots of things could go wrong.

Of course, the Moon is plenty affected by the Sun's gravity. Maybe this video will help.

im wrong ignore that

Gravity is caused by time dilation....

The current gravitational theory and equations are so wrong that they theorized the existence of dark matter. Dark matter is called 'dark' because we have never been able to detect it. It is assumed to exist because it would satisfy the gravitational equations beyond our solar system. Wirhout it, the gravitational equation for our galaxy is off by 2,000%. When you have to make up 2,000% more matter in the universe to resolve an equation, then it is likely that the equation is wrong.

Do you have a link to that plumb line experiment? That sounds interesting, and would be very compelling if repeatable and true

With the work going on at CERN, the theory of the Higgs Boson as a source of sub atomic mass is taking the lead with the results published so far. As for what all that means as mass is related to gravity, not sure? If you are looking for a deeper understanding of it, its one place I would start.

When you smack into something at a high rate of speed, what is it called?

a reply to: SeriouslyDeep

Painful

a reply to: Ksihkehe

a reply to: Ksihkehe

I'm no scientist either, why the dumb questions.

Ok an inverse square function between distance and gravity, that makes sense. But then I wonder, why does air pressure not show an inverse square function between elevation and pressure?

If the mass of the air is negligible what keeps the pressure from dropping at the same rate as gravity?

Or am I totaly wrong in the assumption that pressure, is related to gravity?

It's kind of like whenever I try to imagine mass bending space-time, I wonder how that square function ends inwards, and if there is no gravity at the center, where is everything falling to?


Regarding the tamarack experiment.

Tamarack

originally posted by: Terpene
a reply to: Ksihkehe

a reply to: Ksihkehe

I'm no scientist either, why the dumb questions.

Ok an inverse square function between distance and gravity, that makes sense. But then I wonder, why does air pressure not show an inverse square function between elevation and pressure?

If the mass of the air is negligible what keeps the pressure from dropping at the same rate as gravity?

Or am I totaly wrong in the assumption that pressure, is related to gravity?

It's kind of like whenever I try to imagine mass bending space-time, I wonder how that square function ends inwards, and if there is no gravity at the center, where is everything falling to?


Regarding the tamarack experiment.

Tamarack

I did check the experiments out. It seems they were just simply too inaccurate. Just the tensile strength of the cords used could vary enough that after the stretching they had enough variation to throw things off. There's a lot of calculations before I could say how far off, but since they indicated some experiments showed the pendulums closer then I'd say it's just an inherent flaw in the materials.

The air pressure is really a three dimension thing. It's pushing you at all sides rather than a linear pull. It's no different than water. The effect of gravity on pressure I would speculate is cumulative across the entire spherical mass, while the weight and density of the medium where you happen to be is what determines pressure. The cumulative pull of gravity over you (away from center of mass) is diminished, but increases as you move toward the center as density increases. So air pressure very high up is low as there's little cumulative pressure, but at sea level it's higher (ignoring occasional weather effects that can cause pressure inversions etc this should be constant).

The same goes for water. The surface isn't very highly pressurized, a bit more than air, but the deeper you get the higher the pressure. Boiling water at altitude is at a lower temp because of the pressure. I would imagine that also explains why deep sea thermals are not boiling as well. The increased pressure results in a higher boiling temp ( just looked that up because I was curious, seems the boiling point at those depths is many times highers than sea level).

So the atmospheric pressure is a function of gravity, but it's not a linear gravitational effect. It's more a function of the whole gravitation effect on the pooled mass. Our atmosphere gets weird at the edge of space too. Another thought experiment I've seen is if you drilled a hole directly through the center of the Earth's mass and, minus friction and interference, a ball dropped would accelerate to the center, then past the center to a slightly shorter distance on the opposite side of the earth. It should continue that for a very long time. In a way it's a two dimensional representation of an orbit, a transit? I dunno. Gravity is poorly understood I think. Certainly poorly understood by me. It makes a lot of sense, but also doesn't answer all the questions.