Gravity is an attractive force that affects and is effected by all mass and - in general relativity - energy, pressure and stress. Prefer newtonian-gravity or general-relativity if sensible.

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metamaterials for gravitational waves

Is there such a thing as refractive index of a material for gravitational waves ? How would the index of a material depend on density - Say density of interstellar cloud vs planet vs star vs neutron ...
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2k views

Finding the position of a planet between two other planets of known mass and distance

Here is the question: A planet with mass $m$ and a second with mass $M$ are separated by a distance $d$. A third planet with mass $m_3$ happens to be midway between $M$ and $m$. Where could ...
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1answer
56 views

Could dark energy be linked to dark flow?

I couldn't find any other questions regarding dark flow on Wikipedia, so I'm curious. As far as I can tell, dark energy's existence seems to be hard to explain. Since there may be a couple of ideas ...
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3answers
10k views

How does gravity affect sound waves? [closed]

Someone asked me this question and I don't think I gave him an adequate answer (I was trying to think of the extreme case - that of neutron stars)
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2answers
203 views

Weightlessness and falling sideways

In Season 2, ep 4 of Star talk Radio, host Neil Tyson is talking about the international space station. He mentions that the space station is in a low earth orbit and is falling along the curvature of ...
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2answers
565 views

What method should I use to solve for the final acceleration of a projectile being launched from the earth's surface?

What method should I use to solve for the final acceleration of a projectile being launched from the earth's surface? The question I am working on is: A projectile is launched vertically from ...
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2answers
2k views

Does gravity spread instantly? [duplicate]

Possible Duplicate: The speed of gravity I am real noob in physics, so sorry if this question is really stupid. Today in a casual conversation I claimed that if the sun were to instantly ...
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4answers
425 views

Maximal Gravity

I found this interesting problem in Introduction to Classical Mechanics with Problems and Solutions by David Morin: Given a point $P$ in space, and given a piece of malleable material of ...
6
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3answers
553 views

Why don't astronauts in orbit get stuck to the “ceiling”?

When a shuttle is in orbit, it is essentially rotating around the "centre" of the Earth at a great speed. So why does there seem to be no centrifugal force sticking them to the 'ceiling' of the ...
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4answers
359 views

N particles, will there be any rotation after a period of time or everything will collapse

This is in context of classical Newtonian physics. Consider a system of n different point mass particles. Initially all are spread around on one plane. No particle possess any velocity to begin with. ...
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4answers
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Why can't we feel the Earth turning?

The Earth turns with a very high velocity, around its own axis and around the Sun. So why can't we feel that it's turning, but we can still feel earthquake.
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2answers
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What is the terminal velocity for a mobile phone

You may have seen the story of the iPhone which was dropped from perhaps 13,500 feet by a skydiver - it survived. This made me wonder how to work out the terminal velocity for something like that. ...
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4answers
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what is the difference between a blackhole and a point particle

Theoretically, What is the difference between a black hole and a point particle of certain nonzero mass. Of-course the former exists while its not clear whether the later exists or not, but both have ...
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2answers
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I noticed today that it is easier to open a soda bottle(standard 20 oz) upside-down, why is this?

Am I correct in assuming it is the weight of all that liquid + gravity?
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4answers
444 views

Would there be time dilation at the point where two gravitational fields cancel each other out?

My question is very simple, and most likely a stupid one: One observer is at a point in space were the gravitational force form massive bodies (or a single massive body) cancel each-other out. The ...
3
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2answers
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Can Vesta dominate the orbits of other asteroids?

I think I remember a talk where a professor said that Vesta is a particularly important asteroid because its gravity is strong enough to perturb other asteroids. In spite of Vesta's size, this effect ...
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3answers
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Is the “Great Attractor” an indicator of the “Multiverse”?

I have heard a bit about the Great Attractor (the gravitational anomaly that seems to be "sweeping" our universe in one direction). Someone (and forgive me, I do not recall the specifics) has ...
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1answer
134 views

What is the activity of a planet in a double star system?

If a planet is directly between two stars y distance apart (so it's y/2 from each planet), with velocity x such that x is sufficient to continue orbiting at that distance (y/2), which does it orbit, ...
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2answers
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Gravititonal fields compared to electromagnetic fields - are they infinite in range?

me and my friend has a discussion last night, and he argued that both an electromagnetic field and gravititonal field are infinite in their area of effect, but with diminishing effects as you get ...
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6answers
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Why is gravitation force always attractive?

Why is the gravitational force always attractive? Is there another way to explain this without the curvature of space time? PS: If the simple answer to this question is that mass makes space-time ...
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4answers
4k views

Terminal speed of a body in a gravitational free fall? [closed]

What speed would a small body moving towards a large body reach under gravity alone? More importantly, is there a 'terminal speed' for the small body due to the increasing energy required to ...
11
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5answers
5k views

What happens to light and mass in the center of a black hole?

I know that black holes are "black" because nothing can escape it due to the massive gravity, but I am wondering if there are any theories as to what happens to the light or mass that enters a black ...
4
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1answer
603 views

Artificial Gravity - Spinning Station Questions

I've done a little research but I can't seem to find the answers to these questions in regards to a spinning space station simulating gravity. 1) If we imagine the space station as a hollow doughnut ...
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4answers
388 views

Could dark energy be the effect of gravity at great distances?

This may be a silly question, but is it possible that dark energy and gravity are related to each other? Space-time is deformed everywhere in space by objects with mass. The more massive the object, ...
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2answers
999 views

Impact of gravity on bone structure [closed]

Some suggest that if a human was born and raised in a gravity-less environment their bone structure/strength would be different that for children born on earth. If this is the case do you think this ...
3
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4answers
371 views

existence of other forces obeying inv square law

Is there any restriction in what we know of physics to the existence of other type of forces that obey the inverse square law in 3 dimensions. I mean other than electromagnetic and gravitational. ...
4
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1answer
323 views

Electric potential energy in curved space-time

In flat space-time the electric potential energy between two charges is $\frac{k Q_1 Q_2}{r_{12}}$, where $Q$'s are charges and $r_{12}$ is the distance between them. What would happen if the two ...
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3answers
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How do we determine the mass of a black hole?

Since by definition we cannot observe black holes directly, how do astronomers determine the mass of a black hole? What observational techniques are there that would allow us to determine a black ...
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384 views

Field created by varying Gravitational field

Changing Electric Field causes Magnetic filed and changing Magnetic Field causes Electric Field. Is there anything similar in relation to Gravitational Field? What sort of field is created by varying ...
9
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3answers
228 views

How would two equally massed stars orbit?

In an empty universe, except for two equally massed stars, how would they orbit? Or, for another example, if the earth suddenly grew to be the mass of the sun, how would they orbit, or interact? Would ...
11
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1answer
433 views

Does gravitation of a sphere equal gravitation of a point?

Under Newtonian model of gravity, a perfect sphere creates the same gravitation field as a point mass in its center. General Relativity describes gravitation differently. How much this difference ...
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3answers
411 views

Can a planet cover the whole sky as seen from its satellite

Sorry if this is a trivial question, but I do not know enough physics to answer this on my own. Can there exist a satellite that revolves around a planet so large such that the planet covers the ...
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4answers
2k views

Can the effects of gravity be broken by jumping?

I was having a debate the other day with a work colleague where I explained that gravity is a weak force because it is easily broken. Then I remembered a lecture by someone, I forget who, that ...
3
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2answers
374 views

Astronaut on a rotating asteroid

This might sound like the silliest question ever, but can someone shed some light on what is actually happening in the following situation: There is an asteroid in outer space what is rotating with ...
6
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2answers
253 views

Possibility of “graviballs”?

Looking at the relevant wikipedia page, one can read that the graviton should be massless. Is it 100 % certain that it is massless or is there room in any "nonstandard" models for a tiny non-zero mass ...
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6answers
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How can a black hole emit X-rays?

Considering that a black hole's gravity prevents light from escaping, how can a black hole emit X-rays? Visible light and X-rays are both electromagnetic radiation, shouldn't the black hole's gravity ...
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1answer
222 views

Sun-Earth Virtual Gravitons?

How many virtual gravitons do the sun and earth exchange in one year? What are their wavelengths?
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2answers
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The energy of a Graviton

Maybe another stupid question, but what's the energy of a graviton? Is it $\hbar \omega$? Does it emit gravitons when an apple falls onto the ground, like photons be emitted when an electron transits ...
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1answer
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future light cones and light paths

I understand that an event, in a four dimensional space-time, produces a light cone. As time increases the cones gets larger on either side of the event (past and future). For example the if the sun ...
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A question on a system of particles governed by laws of gravity and electromagnetic field

Consider a system of many point particles each having a certain mass and electric charge and certain initial velocity. This system is completely governed by the laws of gravitation and electromagnetic ...
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2answers
221 views

Question about gravity probe B

I have a question about the gravity probe B experiment. According to this site: http://science.nasa.gov/science-news/science-at-nasa/2011/04may_epic/ The measurements they made confirm Einsteins ...
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2answers
310 views

Would dark matter absorb gravitational waves?

Would the vast and seemingly diffuse clouds of dark matter floating around our galaxy (and most others) absorb gravitational waves? Is this perhaps why we haven't detected any yet?
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0answers
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Calculation of a Gravity Resonance Keyhole

Can anyone describe the mathematics behind the calculation of a resonance keyhole (for a two-body model)? It seems like the size and position of the keyhole should be a function only of mass and ...
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3answers
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Gravitational time dilation at the earth's center

I would like to know what happens with time dilation (relative to surface) at earth's center . There is a way to calculate it? Is time going faster at center of earth? I've made other questions ...
11
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1answer
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Why does gravity need to be quantised?

The electroweak and strong forces seem to be completely different types of forces to gravity. The latter is geometric while the former are not (as far as I'm aware!). So why should they all be ...
3
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1answer
317 views

Olympic games and the local g

As you probably know, the two next Olympic games will take place in London and Rio. Randall, author of xkcd, did an interesting observation (that I had never thought of) in http://xkcd.com/852/ , ...
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1answer
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Voyager local time dilation (caused by gravity)

Voyager I, as an example, taking account gravity and setting aside effects of speed as cause of time dilation. If it is very far away from earth and sun, so then there must be a difference in the ...
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1answer
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Is relativistic motion equivalent to fluctuating gravitational fields?

The theory of relativity makes very precise predictions about how an object's motion through space-time affects the passage of time for both the object and observers in other frames of reference. I ...
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3answers
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Terminal Velocity

Let Suppose a bullet of 2 gram is falling with the speed of 200km/h. Now how can we know the time after which it gains it terminal velocity. Also when it gain its terminal velocity the force of ...
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1answer
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Modeling and Simulating Pendulum Motion

I've been having difficulty creating a mathematical model of a pendulum in my code. While there is plenty of info on general equations describing a the motion of a pendulum, I seem to be having ...