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.

learn more… | top users | synonyms

0
votes
0answers
25 views

Can antimatter becomes black hole? [duplicate]

I know it seems unlikely to accumulate sufficient amount of antimatter to let it collapse under its own weight to become a black hole(maybe the gravity works differently I don't know) since they will ...
3
votes
1answer
68 views

Does my mass really affect objects on the other side of the universe?

I remember hearing back in school that each object is attracted to every other object in the universe. Of course this has to be taken with the understanding that most of those objects have very very ...
0
votes
1answer
40 views

How to calculate the weight in en elevator going upwards / downwards?

When the scale shows higher digits in the elevator, how do I calculate the real weight?
2
votes
0answers
27 views

How to find set point for PID controller for self balancing robot?

I am building a Self balancing robot and needs to tune PID controller to generate PWM signals. My robot chassis is home made and not in perfect alignment. I have placed 6 axis motion sensor on top of ...
0
votes
0answers
44 views

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

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 ...
1
vote
0answers
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 ...
2
votes
1answer
40 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 ...
0
votes
0answers
28 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 ...
-3
votes
2answers
62 views

Why does Earth accelerate every object toward itself with acceleration of $9.8\, m/s^2$ [on hold]

Why Earth accelerates objects due to gravity with $9.8\,\mathrm{m/s}^2$. How to demonstrate that?
2
votes
1answer
94 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 ...
-1
votes
0answers
22 views

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 ...
0
votes
1answer
31 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 ...
1
vote
2answers
56 views

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 ...
1
vote
1answer
49 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 ...
32
votes
10answers
17k views

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 ...
1
vote
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 ...
2
votes
1answer
53 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 ...
-4
votes
0answers
46 views

Gravity. . . is it a force on its own? [closed]

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?
0
votes
0answers
26 views

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, ...
-3
votes
0answers
36 views

Le Sage gravity [closed]

Is there a definitive reason that Le Sage's theory of push gravity, or push gravity in general, can be ruled out as possibility?
0
votes
1answer
81 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 ...
3
votes
2answers
294 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 ...
0
votes
1answer
57 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
votes
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?
4
votes
0answers
83 views

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? ...
2
votes
3answers
210 views

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 ...
3
votes
3answers
501 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 ...
0
votes
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 ...
2
votes
0answers
114 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 ...
0
votes
0answers
14 views

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 ...
1
vote
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 ...
0
votes
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
votes
3answers
273 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 ...
1
vote
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 ...
0
votes
2answers
73 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 ...
9
votes
3answers
3k views

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 ...
3
votes
2answers
174 views

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 ...
1
vote
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
votes
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 ...
0
votes
0answers
39 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?
0
votes
0answers
20 views

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 ...
10
votes
6answers
3k views

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 ...
3
votes
2answers
294 views

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 ...
1
vote
0answers
25 views

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 ...
0
votes
2answers
37 views

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..?
5
votes
3answers
95 views

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
votes
1answer
332 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
votes
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 ...
1
vote
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 ...