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Author Topic: Help me understand the seemingly paradoxical nature of Gravity?  (Read 1904 times)

Offline utopiahell

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Hey friends. I hope someone can help me here because I'm starting to feel like I may be going crazy, and I hope someone can set me straight. My question comes in two parts:

1. Why does gravity often seem to have contradictory effects at different scales?

The Earth is spinning at an extremely fast speed, while also moving through space at an extremely fast speed. This force called Gravity keeps me adhered to the Earth's surface, so it must be quite strong. I can easily imagine how strong a force would have to be to keep a tiny object adhered to the surface of a basketball while it was both spinning and moving. So I can empirically deduce that the pull of gravity must be extremely strong.

However, this extremely strong force is also what keeps the moon orbiting the Earth, and the planets of our solar system orbiting the sun. The moon orbits the Earth at a relatively constant distance, and the planets orbit the sun at a relatively constant distance. I understand that the distances vary slightly as the orbits are actually elliptical, but my point is that the planets are not pulled towards the sun, and the moon is not pulled towards the Earth. Man has observed Mercury, for example, orbiting the sun for millenia, and it has apparently failed to be pulled into the sun by the force of the Sun's massive gravitational field, which paradoxically is strong enough to act on a planet such as Neptune, which is orbiting the sun at a distance that is orders of magnitude larger than Mercury's distance from the Sun.

So gravity simultaneously pulls me towards the Earth with such immense force that I adhere to it despite the massive motion of the Earth, yet also keeps the planets and moon orbiting at a relatively constant distance, failing to pull them the same way I am apparently pulled towards the Earth. What gives? How can gravity apparently pull sometimes, yet paradoxically also be the force that allows planets and moons to obtain stable orbits?

2. The Earth is the only object that I can empirically verify as possessing Gravity.


In my physics classes, when learning about Gravity, someone of course asked the obvious question of, "Why don't mountains have gravity?" or why we fail to observe gravitational fields forming around sufficiently large masses on Earth. The answer I received for this is that the gravity of the Earth is so extreme that it dwarfs the force of gravity of these smaller objects and renders them negligible.

This seems to be in opposition to the apparent fact that perpendicular forces are supposed to not effect each other in this universe. For example, you are most likely familiar with the thought experiment of a car moving forward on a frictionless surface at 100 mph. This car is then struck from the side at a perfect 90 degree angle to it's current path by another object. I have always learned that on this frictionless plane, the car would still be moving forward at 100 mph, because the two perpendicular forces do not affect each other - it would just now also have additional momentum pushing it along the horizontal axis.

If this is the case, then sufficiently large masses on Earth should have demonstrable gravitational fields. The gravity of the Earth is pulling down (we'll call this the Y axis), but a sufficiently large mass, such as a massive lead cube, would, if you were holding an object next to it, be exerting it's own gravity horizontally (on the x axis). The vectors of these two forces are perpendicular, and thus should not cancel each other out.

To give a basic example, if you were throwing a football past a 200 x 200 ft. lead cube, the gravity of the Earth would be pulling the football down, but the gravity of the cube should also be able to pull the football towards it, to the left or to the right depending on where you are. This obviously does not happen. On a more practical level, it seems like objects of normal mass should be able to attract sufficiently small masses, as long as the ratio of their masses is similar to the ratio of my mass to the Earth's. This also does not happen.

If perpendicular forces cannot cancel each other out, why can't we observe the gravitational force of masses on Earth?

I sincerely look forward to any input someone can give me on these questions, as they have been vexing me for some time and despite a decent (albeit elementary) education in basic physics, I really cannot explain this.

Thanks!


 

Offline alancalverd

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1. Why does gravity often seem to have contradictory effects at different scales?
It doesn't. The fundamental equation F = GMm/r2 apparently applies to all objects we have ever observed.

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In my physics classes, when learning about Gravity, someone of course asked the obvious question of, "Why don't mountains have gravity?" or why we fail to observe gravitational fields forming around sufficiently large masses on Earth. The answer I received for this is that the gravity of the Earth is so extreme that it dwarfs the force of gravity of these smaller objects and renders them negligible.
Sadly, the quality of physics education seems to have gone down the drain - at least wherever you were educated. It's not easy, but it has been done umpteen times.
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Nevil Maskelyne’s 1774 experiment on the Scottish mountain Schiehallion set out to derive the mean density of the Earth, from astronomical observations of the deflection of the vertical and calculation of the mountain’s relative gravitational attraction.
was in my school textbooks, and
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The Cavendish experiment, performed in 1797–1798 by British scientist Henry Cavendish, was the first experiment to measure the force of gravity between masses in the laboratory[1] and the first to yield accurate values for the gravitational constant (G).

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If perpendicular forces cannot cancel each other out, why can't we observe the gravitational force of masses on Earth?
You have hit on the basis of both the Maskelyne and Cavendish experiments. Just 250 years too late for a Nobel prize, but not too late to complain about your education!
 

Offline stacyjones

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http://www.nasa.gov/mission_pages/gpb/gpb_results.html

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"Imagine the Earth as if it were immersed in honey. As the planet rotates, the honey around it would swirl, and it's the same with space and time," said Francis Everitt, GP-B principal investigator at Stanford University

Honey has mass and so does the dark matter. Dark matter fills 'empty' space and is displaced by matter. The dark matter displaced by the Earth pushes back and exerts pressure toward the Earth. The dark matter displaced by the Earth pushing back and exerting pressure toward the Earth is gravity.

Think of the dark matter as being a supersolid the Earth moves through and displaces. The supersolid nature of the dark matter causes it to push back when displaced. This pushing back is what keeps you tied to the Earth. This pushing back is gravity.
« Last Edit: 07/05/2016 20:37:35 by stacyjones »
 

Offline utopiahell

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Alancalverd, cool answer, I will look into these things tonight when I get off work. Since you seem to have some knowledge, would you mind addressing the first part of my question? If the effect of gravity is universal, why has the sun not pulled in the inner planets after at least two to three thousand years of humans observing them orbiting in a relatively constant state?

Stacyjones, I'll also take a look at your answer after I get off work tonight.
 

Offline jeffreyH

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Alan I would definitely listen to. Stacyjones I would ignore. That is my advice to you utopiahell. Take it or leave it as you wish.
 

Offline stacyjones

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Or, you could correctly understand what occurs physically in nature which causes gravity.
 

Offline alancalverd

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If the effect of gravity is universal, why has the sun not pulled in the inner planets after at least two to three thousand years of humans observing them orbiting in a relatively constant state?

It's down to the perpendicularity question that you so acutely put. Imagine a hunk of rock m hurtling through space and coming close to a much larger one M. Consider the large one as stationary. Then the small one has a velocity that can be resolved into two components, a (towards M) and b (perpendicular to a). The overall assembly has angular momentum around the mutual center of gravity, if b is not zero. Angular momentum is conserved, so m orbits around M with a constant tangential speed b. If m moved closer to M, conservation of angular momentum would require b to increase, with a resulting increase in centrifugal force that would push m outwards again.

It's easier to imagine special case of a circular orbit  rather than the general case of an ellipse, but Kepler's discovered laws of planetary motion are actually numerical solutions of the general orbital equations that you can derive from the gravitational inverse square law and simple mechanics of rotating systems.

The problem with SJ's hypothesis is that he can't or won't state the density, viscosity, or elastic modulus of his celestial honey, and all attempts to measure its properties suggest it doesn't exist.
« Last Edit: 08/05/2016 11:15:44 by alancalverd »
 

Offline stacyjones

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The problem with SJ's hypothesis is that he can't or won't state the density, viscosity, or elastic modulus of his celestial honey, and all attempts to measure its properties suggest it doesn't exist.

The Gravity Probe B experiment measured the honey.

http://www.nasa.gov/mission_pages/gpb/gpb_results.html

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"Imagine the Earth as if it were immersed in honey. As the planet rotates, the honey around it would swirl, and it's the same with space and time," said Francis Everitt, GP-B principal investigator at Stanford University.

Honey has mass and so does the strongly interacting dark matter which fills 'empty' space.  The swirl is the state of displacement of the strongly interacting dark matter.
 

Offline McQueen

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Unlike Einstein and Nobel prize winner  Neils Bohr, Sir Isaac Newton was never willing to hypotheses on a physical phenomenon he suspected existed but did not have factual evidence of "Hypotheses non fingo".  Therefore although he strongly felt that his theory might in fact be the solution he did not hypothesize that it might be fact.  He felt that his observations and calculations bore out the fact that gravity existed in everything , from a feather to an iron ball! And that the force exerted by gravity depended solely upon the density and mass of the object. This is in fact true. Yet, in spite of all this no solution  as to why gravity behaves as it does has ever been found to date. Here are Sir Isaac Newton's thoughts on gravity. Notice how powerful his language is: "penetrates to the very centre of stars and planets !" :

“Hitherto we have explained the phenomena of the heavens and of our sea by the power of gravity, but have not yet assigned the cause of this power. This is certain, that it must proceed from a cause that penetrates to the very centers of the sun and the planets, without suffering the least diminution of its force; that operates not according to the quantity of the surfaces of the particles upon which it acts (as mechanical causes used to do) , but according to the quantity of solid matter which they contain, and propagates its virtue on all sides to great distances , decreasing always in the duplicate proportion of the distances……But hitherto I have not been able to discover the cause of those properties of gravity from phenomena, and I frame no hypotheses (Hypotheses non fingo); for whatever is not deduced from the phenomena is to be called a hypotheses, whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy. “

The Gestalt Aether Theory of Gravity corresponds extremely closely, in every regard, with the musings of Sir Isaac Newton.  It also clearly illustrates that every object no matter how insignificant is also affected by the force of gravity.  So no matter big or small or tiny and gigantic, the same rules apply. Don't be deceived by the seemingly emptiness and vastness of space. Gravity, according to Newton ( not Einstein) still rules.
« Last Edit: 08/05/2016 13:25:28 by McQueen »
 

Offline stacyjones

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https://en.wikipedia.org/wiki/Aether_theories#Luminiferous_aether

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Isaac Newton suggests the existence of an aether in The Third Book of Opticks (1718): "Doth not this aethereal medium in passing out of water, glass, crystal, and other compact and dense bodies in empty spaces, grow denser and denser by degrees, and by that means refract the rays of light not in a point, but by bending them gradually in curve lines? ...Is not this medium much rarer within the dense bodies of the Sun, stars, planets and comets, than in the empty celestial space between them? And in passing from them to great distances, doth it not grow denser and denser perpetually, and thereby cause the gravity of those great bodies towards one another, and of their parts towards the bodies; every body endeavouring to go from the denser parts of the medium towards the rarer?"

Newton is referring to the state of displacement of the aether.

The aether displaced by the Earth pushing back and exerting pressure toward the Earth is gravity.
 

Offline PmbPhy

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Quote from: utopiahell
Hey friends. I hope someone can help me here because I'm starting to feel like I may be going crazy, and I hope someone can set me straight.
First let me welcome you to the forum. Welcome! :) And we'll be glad to help you. After all, that's why we're here.

Next, listen to Jeff's advice and ignore what stacyjones wrote regarding dark matter. It's all nonsense.

Quote from: utopiahell
My question comes in two parts:

1. Why does gravity often seem to have contradictory effects at different scales?
As Alan said, any thing that "seems" to have contradictory effects is merely due to your lack of understanding of gravity which we'll help you to correct.

Quote from: utopiahell
The Earth is spinning at an extremely fast speed, while also moving through space at an extremely fast speed. This force called Gravity keeps me adhered to the Earth's surface, so it must be quite strong.
You have an incorrect impression here. The "speed" that you mention regards the speed at which the surface of the earth moves relative to the local inertial frame. But that speed as little effect on the force which seemingly is working against the force of the Earth's gravitational force. That's the centrifugal force and its proportional to the square of the angular velocity of the Earth and the Earth's radius. Given the large radius of the Earth and the very small angular velocity means that the centripetal acceleration is very small when compared to the gravitational force.

Quote from: utopiahell
I can easily imagine how strong a force would have to be to keep a tiny object adhered to the surface of a basketball while it was both spinning and moving. So I can empirically deduce that the pull of gravity must be extremely strong.
Here the centripetal force of a particle sitting on the ball's surface is much larger than the gravitational force due to just the ball.

Quote from: utopiahell
However, this extremely strong force is also what keeps the moon orbiting the Earth, and the planets of our solar system orbiting the sun.
The gravitational force on a person due to the Earth's gravitational field at the Earth's surface is not as strong as you've been thinking. Force is mass times acceleration, i.e. F = ma where here a = g = the acceleration due to the gravity. It's only 9.8 m/s. In terms of pounds the force on a body is merely it's weight. I wouldn't call your weight "extremely strong," would you?

Quote from: utopiahell
The moon orbits the Earth at a relatively constant distance, and the planets orbit the sun at a relatively constant distance. I understand that the distances vary slightly as the orbits are actually elliptical, but my point is that the planets are not pulled towards the sun, and the moon is not pulled towards the Earth.
Here, your quite wrong. All bodies exert a gravitational force on all other bodies.

Quote from: utopiahell
Man has observed Mercury, for example, orbiting the sun for millenia, and it has apparently failed to be pulled into the sun by the force of the Sun's massive gravitational field, which paradoxically is strong enough to act on a planet such as Neptune, which is orbiting the sun at a distance that is orders of magnitude larger than Mercury's distance from the Sun.
That's because the speeds of the planets are such that the force of gravity is balanced against the centrifugal force. Billions of years ago all bodies that were moving either too slow was pulled into the sun and all matter that were moving too slow and those bodies which were moving too fast left our solar system. If would due you a world of  good to sit down and work out these calculations with pencil, paper and calculator and see for yourself.

Quote from: utopiahell
2. The Earth is the only object that I can empirically verify as possessing Gravity. [/b]
That's hardly true. What do you think's holding the planets in orbit around the Sun?

Quote from: utopiahell
In my physics classes, when learning about Gravity, someone of course asked the obvious question of, "Why don't mountains have gravity?" or why we fail to observe gravitational fields forming around sufficiently large masses on Earth. The answer I received for this is that the gravity of the Earth is so extreme that it dwarfs the force of gravity of these smaller objects and renders them negligible.
That's exactly true. Try making the calculations for yourself.

Quote from: utopiahell
This seems to be in opposition to the apparent fact that perpendicular forces are supposed to not effect each other in this universe.
The gravitational force isn't  perpendicular, its a central force which means that the forces acting between two bodies is towards each other.
 

Offline stacyjones

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Next, listen to Jeff's advice and ignore what stacyjones wrote regarding dark matter. It's all nonsense.

Or, you can correctly understand what occurs physically in nature which causes gravity. 'Empty' space has mass which is displaced by matter. The Earth displaces the mass which fills 'empty' space. The mass which fills 'empty' space pushes back and exerts pressure toward the Earth. The mass which fills 'empty' space pushing back and exerting pressure toward the Earth is gravity.
 

Offline PmbPhy

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Quote from: stacyjones
The aether displaced by the Earth pushing back and exerting pressure toward the Earth is gravity.
It's responses like this why Jeff and I said to ignore you. There is no aether. It doesn't exist. All attempts to find it failed, If it had the properties that it was defined to have then it would have been detected. Therefore if something exists and it can't be observed then it's not falsifiable and therefore does not belong to any physical theory. And even if it did then your belief about its properties are incorrect. That's all I'm going to say about these aether ideas. They're a waste of time.
 

Offline stacyjones

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It's responses like this why Jeff and I said to ignore you. There is no aether. It doesn't exist. All attempts to find it failed, If it had the properties that it was defined to have then it would have been detected. Therefore if something exists and it can't be observed then it's not falsifiable and therefore does not belong to any physical theory. And even if it did then your belief about its properties are incorrect. That's all I'm going to say about these aether ideas. They're a waste of time.


http://www.nasa.gov/mission_pages/gpb/gpb_results.html

Quote
"Imagine the Earth as if it were immersed in honey. As the planet rotates, the honey around it would swirl, and it's the same with space and time," said Francis Everitt, GP-B principal investigator at Stanford University

Honey has mass and so does the dark matter. Dark matter fills 'empty' space and is displaced by matter. The dark matter displaced by the Earth pushes back and exerts pressure toward the Earth. The dark matter displaced by the Earth pushing back and exerting pressure toward the Earth is gravity.
 

Offline alancalverd

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The Gravity Probe B experiment measured the honey.
So why don't you just tell us its viscosity, density and elastic modulus? What else is there to measure?
 

Offline PmbPhy

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The Gravity Probe B experiment measured the honey.
So why don't you just tell us its viscosity, density and elastic modulus? What else is there to measure?
I'm sure you know that the best thing to do when you run into people who use meaningless arguments using the aether (that doesn't exist) as explanations. Unless they're asking a question, you ignore them.
 

Offline stacyjones

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https://en.wikipedia.org/wiki/Aether_theories#Quantum_vacuum

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Robert B. Laughlin, Nobel Laureate in Physics, endowed chair in physics, Stanford University, had this to say about ether in contemporary theoretical physics:
The modern concept of the vacuum of space, confirmed every day by experiment, is a relativistic ether. But we do not call it this because it is taboo.
 

Offline alancalverd

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I haven't seen Robert for several years, but if you'd care to tell me his measurements of the viscosity, density and elastic modulus of the aether, I'm prepared to believe them. If not, I must continue to assume that you haven't understood what he is talking about.
 

Offline stacyjones

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Can you explain to me how, "The modern concept of the vacuum of space, confirmed every day by experiment, is a relativistic ether" is interpreted to mean there is no such thing as an ether? Is the issue with the term?

Let's make up a new term in order to start fresh. I will label the mass which fills 'empty' space which is displaced by the particles of matter which exist in it and move through it the 'rehtea'.

I think it's safe to say after over 30 years and more than a billion dollars and there being zero evidence of WIMPs we can move beyond that incorrect notion. If you want to continue to believe in something that billions of dollars and decades have been spent looking for with zero evidence of it then that is your choice.

I'm going to take it a step further and say that the whole notion of dark matter as a clump of stuff that travels with the matter is incorrect.

Rehtea has mass, physically occupies three dimensional space and is displaced by the particles of matter which exist in it and move through it.

The "missing mass" is the mass of the rehtea which is connected to and neighbors the matter which is displaced by the matter.

The Milky Way's halo is lopsided due to the matter in the Milky Way moving through and displacing the rehtea, analogous to a submarine moving through and displacing the water.
« Last Edit: 08/05/2016 21:36:51 by stacyjones »
 

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