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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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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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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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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1answer
49 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
48 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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68 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? ...
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31 views

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

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 ...
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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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31 views

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

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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117 views

What is the peak moment of a hook [on hold]

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
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 ...
2
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0answers
95 views

$AdS_2$ Black Hole [on hold]

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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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 ...
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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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1answer
40 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
76 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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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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2answers
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3
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2answers
287 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 ...
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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 ...
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2answers
36 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..?
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2answers
71 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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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 ...
2
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0answers
23 views

What would be the shape of a candle in a zero gravity environment? [duplicate]

What would be the exact shape of a burning candle if it is placed in a zero gravity environment...I am not able to determine the way the fire and the candle aligns.. Please help me out!
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2answers
72 views

Why do we feel resistance to gravity rather than the acceleration of gravity?

What's the reason it behaves differently from all other forces? What I mean is, if you're in orbit you're accelerating toward the earth at almost 9.8m/s^2, but you feel nothing. If you are riding a ...
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1answer
49 views

Two spherically symmetric shells of matter collapsing into a black hole

Suppose I have a thin spherically symmetric shell of matter of (rest) mass $M$ that collapses to form a black hole, and later a second thin spherical shell of mass (rest) $M'$, concentric to the ...
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35 views

Measuring Hawking radiation after the coordinate transformation

If an observer can measure the Hawking radiation or surface gravity in his co-moving/rest frame, what happens when we make a coordinate transformation to a moving frame of reference? Can we make such ...
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1answer
44 views

Does Earth also move due to some electrostatic forces?

Does the earth experience some electrostatic forces due to other planets...which also make it move? My question is..whether the earth also moves due to electrostatic force of attraction or only due ...
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1answer
56 views

are spacetime and gravitons one in the same? [closed]

I ask because it seems to me with my admittedly limited knowledge that this doesn't necessarily contradict any widely accepted theory. In fact it would help explain a few incomplete theories. Does ...
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1answer
43 views

Converging light

Imagine that we emit a light pulse. As is the nature of light, it will expand. However, light is affected by gravitational fields and light has its own. Therefore, will the light converge given ...
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1answer
34 views

Is force exerted by Earth different for different mass?

We know Earth pulls every object by the same acceleration $g$ (say). force exerted by earth $F=m\cdot g$ (with $m$ the mass of the body), so, if $g$ is constant then $F$ is directly proportional to ...
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1answer
49 views

Gravitational Force vs. Centripetal Acceleration

Can someone please explain this conceptually: Suppose we have two probes, one one the surface of the earth and one in geosynchronous orbit. Since $a_c = \omega^2r$, the probe that is further out, ...
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42 views

Is the acceleration of a soap bubble the standard value of gravitational acceleration?

Is the acceleration of a basic soap bubble the same as the standard value of gravitational acceleration 9.81 m/s^2 when it is dropping in a windless space? I have used the Newton's 2nd law to prove ...
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1answer
63 views

Where will the cloth fold? [closed]

Here's a picture: There is a planet where there is no air, and nothing else there at all except the force of gravity and a surface. On this planet, there is a single post, placed perfectly ...
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High density vessel's effect on gravity

How would a vessel with a very dense mass ( $M=xBH$ where $x<1$, $BH=$density of black hole) a fraction of that of a black hole behave in space? What would happen to time inside that vessel? If an ...
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1answer
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Could the 4 Forces Split Off or “Decay” into Other Forces in the Distant Future? [duplicate]

From my basic understanding of popular-level physics articles and books and such, the 4 forces (Electromagnetism, Gravity, Strong and Weak Force) used to be 1 force in the early universe, then split ...
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5answers
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Which way will the pencil fall?

Let's say you had a perfect pencil, with a point which was just that one point (see this question). The pencil's mass was perfectly distributed, and there are no flaws in the craftsmanship. Let's say ...
2
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1answer
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Mass Distribution Inside Sphere with Relativity

(Shell Theorem) If a mass is spherically symmetrically distributed within a spherical region, an observer measuring the gravitational pull from that spherical region would not know how the mass is ...
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1answer
79 views

Force of Gravitational attraction between the ring and the sphere? [closed]

Let us say a uniform ring of mass m and radius 3a is kept above a sphere of mass M and radius 3a at a distance of 4a such that line joining the centres of ring and sphere is perpendicular to the plane ...
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2answers
48 views

what is the result of change in gravitational flux?

As a change in magnetic flux results in induced EMF (electromotive force) likewise what is the result of a change in gravitational flux? UPDATE: Gravitational flux according to me has only ...
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1answer
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Normal force on a banked road & why it's larger than the gravitational force here

Please read this: http://www.askiitians.com/iit-jee-physics/mechanics/banking-of-roads.aspx From my understanding of normal forces, they are a reaction to gravitational or other forces. When a force ...
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3answers
94 views

Could black holes be driving the expanding universe (dark energy)?

I would like to start be saying I'm no Physicist. Anyway, my question is: Could black holes be driving the expanding universe (dark energy)? When I think of the image that the effect of massive ...
2
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0answers
32 views

Maximum Power transmitted using General Relativity waves - cf Schwinger limit

In Electromagnetism, QED says that the linearity of Maxwell's equations comes to an end when field strengths approach the Schwinger limit. Its about 10^18 V/m. What is the corresponding formula for ...
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3answers
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Negative density solutions of the Poisson's Equation for polytropic gas (aka Lane-Emden Equation)

Question: What does it mean by when we obtain negative density for specific region in space as a solution of Poisson's equations? I will explain the situation as detailed as possible, so that anyone ...
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1answer
34 views

Working out length of taut rope orbiting the earth remaining straight and radially directed [closed]

A taut rope is orbiting the earth with angular velocity $a$. It remains straight and radially directed. If the midpoint is located at radius $r$, find the length of the rope. I can't even imagine ...
2
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3answers
171 views

Where does air pressure come from?

Where does air pressure come from? I thought it was from gravity or the speed of the gas resulting from its heat. However, analyzing my own hypotheses, I think that my 'heat conjecture' is probably ...
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value of $n$ in modified gravity model

In the modified gravitational model $ f(R)=R+\lambda{R_{0}}\left(\left(1+\frac{R^{2}}{R_{0}^{2}}\right)^{-n}-1\right) $ Are there any restrictions on the value on $n$. Also is this model valid for ...
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Is the planet Mesklin as described in Hal Clement's Mission of Gravity correct?

The book Mission of Gravity describes a planet with a mass of 16 times Jupiter spinning at a rate of one revolution every 17.75 minutes. This causes it to stretch out into an oblate spheroid and has ...