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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How stable is a tablespoon of neutrons once removed from a neutron star?

I've often heard public lectures describing the degenerate, exotic matter left behind after a star collapses but fails to go supernova; one that has found its way to become a neutron star. The speaker ...
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116 views

Can one model a spiral galaxy with a similar manifold to one for a whirlpool?

My question is more of a phenomenological question than literal, since the forces involved are very different. When one looks at the distortions (or wrinkles or whatever you wish to call them) in the ...
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1answer
32 views

Work in gravitational field

I was doing a test a few days ago and there was a fairly simple task involving gravity basics. The task asks me to calculate the work done by moving an Earth's artificial satellite from a stationary ...
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22 views

Why gauge field should be vanishing on horizon?

When considering an AdS spacetime including a black hole, matter field and gauge field, the value of temporal component $A_t$ of the gauge potential $A_\mu$ on horizon always is set be zero, even the ...
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Why does Earth accelerate every object toward itself with acceleration of $9.8\, m/s^2$

Why Earth accelerates objects due to gravity with $9.8\,\mathrm{m/s}^2$. How to demonstrate that?
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1answer
86 views

If the effects of gravity cannot travel faster than the “c”, does this mean we are only gravitationally bound by masses in our observable universe?

I'm 17 and fascinated by the differences and omissions Newton made in his equations of motion. However it makes sense that gravity can't travel faster than light because of the force-carrying ...
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Is it possible that gravity is created by the empty space in all matter? [on hold]

Everything is made up of atoms, which are made up of 99% empty space. Thus, everything is made up of 99% empty space; furthermore everything has gravity. Given this, is it a plausible theory to ...
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1answer
30 views

The significance of the pressure term within the momentum-energy tensor [duplicate]

EDIT: this question is based around my notion regarding the possible role of potential energy in the momentum energy tensor T$_{\mu\nu}$, The answer below resolves the question and I have deleted ...
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2answers
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Why do planets move in fixed orbits?

Is it because the bending of space that occurs around the Sun creates a force acting on the planet which accelerates it towards the Sun (F=ma) while the planet has a tendency to move in a straight ...
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1answer
48 views

How much is time slowed down inside a planet or star?

An answer to What would be the rate of acceleration from gravity in a hollow sphere? states "that according to General Relativity time passes more slowly inside a hollow massive sphere than it does ...
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10answers
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How exactly does curved space-time describe the force of gravity?

I understand that people explain (in layman's terms at least) that the presence of mass "warps" space-time geometry, and this causes gravity. I have also of course heard the analogy of a blanket or ...
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1answer
116 views

Spiral galaxies and gravity lenses

Spiral Galaxies must have a great deal more mass than elliptical galaxies of the same size in order to account for the flat velocity curve. I've seen references of eight to ten times the visible ...
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1answer
52 views

How would gravity work in a Dyson's shell?

A Dyson's shell is often depicted in fiction, sometimes with inhabitants dwelling on the inside of the shell. Has anyone ever proposed how gravity would work inside of a Dyson's shell? Centrifugal ...
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Gravity. . . is it a force on its own? [on hold]

What are the chances that gravity is in fact the by-product of another characteristic of the functioning universe and not a force unto itself?
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1. How is Newtonian calculations compatible with curved spacetime? and 2. multiple competing reference frames for gravity [duplicate]

Since spacetime is curved, and since the measurement of distance on a curve is along a geodesic, how is it that Newtonian (non-curved) physics can be successfully deployed to calculate distances, ...
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0answers
36 views

Le Sage gravity [on hold]

Is there a definitive reason that Le Sage's theory of push gravity, or push gravity in general, can be ruled out as possibility?
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1answer
79 views

Isolation of a Physical System and Energy

I'm trying to grasp basic concepts of energy and i have a little doubt regarding conservation of energy. According to Feynman book and Wikipedia, the Law of Conservation of Energy states that ...
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2answers
289 views

What is conformal gauge?

I often see in physics articles on gravity such notion as conformal gauge and Weyl transformation. They use Conformal gauge to change coordinates to transform metrics from arbitrary $$ds^2=g_{\mu ...
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1answer
54 views

Shape of galaxies [duplicate]

i want to know why galaxies are spiral in nature.. let us say there is some sort of intense mass (black hole?) at the centre of our milky way galaxy. the intense gravitaional pull is keeping evey ...
2
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1answer
52 views

How is it we have helium on earth?

Earth gravity isn't strong enougth to hold helium so we are loosing it constantly. If earth assembled out of space dust how come we have helium? Where did it come from?
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Is MOND dead or still being actively researched?

This may be an opinion based question, and if so I shall remove it, but is MOND, Modified Newtonion Dynamics, pretty much dead as both a theory/ hypothesis and also as an active research subject? ...
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3answers
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Einsteins gravity Space time

I'm having a difficulty in understanding Einstein's version of gravity as "space time curvature" (I could be a total physics idiot, please point out !). How does an object on the surface of earth ...
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0answers
32 views

if gravity travelled faster than light, what would the implications be? [closed]

I know that some weird stuff might take effect in the long term outside of the observable universe affecting us and I do have a lot of ambitious, intuitive guesses based on my qualitative ...
3
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3answers
491 views

Is the Moon freely falling towards the Earth?

The Moon is revolving around the Earth and its centripetal acceleration is towards the Earth. Does it mean that the Moon is freely falling towards Earth? What is the cause of the Moon orbiting around ...
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0answers
36 views

How black hole lose mass? [duplicate]

Even in empty space virtual particles can constantly pop in and out of existence in pairs, when 1 of the pair fall into the black hole while the other escape this is hawking radiation but black hole ...
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0answers
105 views

$AdS_2$ Black Hole [closed]

I know that $AdS_2$ black hole has the following metric: $$ ds^2=(r^2-a^2)dt^2+\frac{dr^2}{r^2-a^2}.\tag{1} $$ Here $a$ is constant. On the other hand I am regularly facing with the following ...
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31 views

What is the theoretically lowest limbo bar which could be done by humans? [closed]

Note: This may be more of a biology question. Let's say you had some limbo bar, and a person who was about average in flexibility, height, weight, etc. What would be the lowest limbo bar you could ...
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126 views

What is the peak moment of a hook [closed]

BSD What is the peak moment of a hook with a downward force. The question is illustrated in the pic below. Its from a test I had and I wanted to know if I got the wrong answer. Any suggestions on ...
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0answers
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How this tube rotates? [duplicate]

I recently seen a video where a tube is spin into space. When it starts to rotate, it keeps continuously to rotate along the axis of 180 degrees clockwise, then 180 counter-clockwise and so on. The ...
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1answer
63 views

Propagating higher order Hermite Gaussian modes. What are complex amplitude coefficients?

I've been tasked with writing a code (in MatLab, but I'm currently using Mathematica because I don't know MatLab %\ ...) to simulate the propagation of a Gaussian beam. I don't really know anything ...
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0answers
37 views

Janibekov Effect [duplicate]

Recently I've learned about Janibekov effect, which looks like magic. What's the explanation behind it? I remeber from school that if no force is applied then object should keep still or continue ...
2
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3answers
269 views

Power to suspend a mass in air

How much power is needed to suspend a mass in the air? The four parts below deal with the same problem. I post them all here, should there be some subtle things I didn't see. The textbook problem A ...
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1answer
41 views

What is the pressure at the center of the Earth? (Or a neutron star)

The center of the Earth has microgravity and is thought to be solid and almost 6000 degrees hot. What is the pressure like there? The confusing thing, for the common man I suppose, is that there's no ...
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2answers
72 views

Gravitational force in a building

Suppose that a person is standing on the top of a multi storey building and at an instant earth's gravitational pull becomes zero.What will happen in the next instant? (Consider only earth's gravity ...
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3answers
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Is gravitational time dilation different from other forms of time dilation?

Is gravitational time dilation caused by gravity, or is it an effect of the inertial force caused by gravity? Is gravitational time dilation fundamentally different from time dilation due to ...
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2answers
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What is the physics of tilt compensation of an electronic compass

This question concerns the physics behind the implementation of electronic compasses to find the orientation of a device. In the robotics community, 3-axis magnetometers are often used for this ...
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2answers
77 views

Can gravity be interpreted as the acceleration of spacetime towards an object? [closed]

Greetings StackExchange! We were having a conversation with a peer about stupid ways of interpreting theories. We would go to and fro with an interpretations, but we would always find a way to ...
3
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1answer
38 views

Light trajectory

We have observed stars where "we should not" Some people say that gravity can alter light trajectory. Some people say that gravity actually alter the space on which light travels. Which one is ...
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0answers
38 views

Star vs Blackhole - Accretion Disk

Simple question: can we prove that what we call today a "star" is not a accretion disk of a "tiny" black hole that happens to rotate in all the 3 axis?
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0answers
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In Which Position A Co-passanger should Sit On A Turning Bike

Pardon me for this very basic mechanical science question. But I just want to clear my doubt it. Whenever I sit a behind someone on a bike I get confused when the the bike has to take a sharp turn. I ...
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6answers
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What will happen if a ball of ice with the mass of sun is thrown into the sun?

The question is a bit unrealistic with its circumstances but lets assume there is a bucket of ice cooled down to about absolute zero and is about 1000 km away (all around the sun) from sun and moving ...
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2answers
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How does gravity increase (or, at least, not-decrease) entropy?

I'm a total physics n00b (i.e. I only know the physics as taught in IT grades, and don't remember much of it), and was talking about entropy (initially, not with the physical implications). My friend ...
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Masking tape-flexometer vs gravity? [closed]

For my work I been trying to find the best way to hang a flexometer on to the wall using masking tape, the reason for this is to be able to measure the height of people for a survey. I been trying ...
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2answers
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Can we make a force which can oppose earth gravity? [duplicate]

IF We are standing on a earth.then some force (gravity of earth) is pulling us down..then "cant we make a force which can oppose gravity..? Cant we make a object of zero mass..?
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3answers
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How is the conservation of momentum satisfied in long-range attraction such as electromagnetism and gravity?

I'm not a physicist, but my understanding is that electromagnetism (including attraction between opposite charges) is mediated by the photon, and gravity is probably (hypothetized to be?) mediated by ...
6
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1answer
331 views

Alcubierre warp bubble effect on gravity and space

I read the question Faster-than-light communication using Alcubierre warp drive metric around a single qubit?, and these questions came to mind: What kind of impact would an Alcubierre warp bubble ...
3
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1answer
140 views

Does all matter emit gravitational waves all the time?

I understand that gravitational force is a result of the curvature of spacetime and that the analogy with electromagnetic waves falls apart at a certain point. However, I have been confused when ...
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3answers
119 views

How strong must gravity be to stretch time?

I'm not sure if this is true or not but I heard that gravity has the ability to stretch time, and I was wandering if this is true. If so, how intense/powerful does the gravitational force have to be ...
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0answers
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What level of mathematics would I need to understand the physics of a black hole? [duplicate]

I recently went to go see the movie Interstellar and was awed by the visualizations of the wormhole and the black hole Gargantua. I read that noted physicist Kip Thorne was a consulting producer on ...