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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Have hypothetical particles with gravitational mass unequal to their inertial mass been proposed in the past, e.g. as candidates for dark matter?

This is a question about history. To my understanding the equivalence of intertial and gravitational mass for all known particles is a weird empirical coincidence that has been confirmed to high ...
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Would a person in a gravity well observe the sky as rapidly moving due to time shift?

Inspired by the movie Interstellar (2014) - I was wondering about the crew on the surface of the planet which was deep in the gravity field of the black hole (Gargantua) - if they would look up at the ...
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Thermal AdS3 in Chern Simons

I am currently working with (2+1) gravity in Chern-Simons formulation and I have a question about thermal AdS. The way I understand that one retrieves thermal AdS is by Wick rotation and ...
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180 views

Gravitational constant, $G$, What if it is not Constant?

The question is on title; What if Gravitational Constant, $G$, is not constant? Let's skip all the local consequences if it would suddenly change, like asked here; Can gravitational constant be ...
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How can the speed and the mechanics of light be similar to the speed and the mechanics of gravity? [duplicate]

How can the speed and the mechanics of light be similar to the speed and the mechanics of gravity? Most say that light cannot escape a black hole. Then gravity cannot escape a black hole either, so ...
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Changing orbit of a space shuttle

In the figure here, a space shuttle is initially in a circular orbit of radius r about Earth. At point P, the pilot briefly fires a forward-pointing thruster to decrease the shuttle’s kinetic energy K ...
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Gravitational waves and time

Two questions. It is said that time can only go slower in gravity fields and if you move faster. I have heard that when a gravitational wave pass earth then the space/time vibrate and time change ...
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21 views

Equation for Turning Projectile

I'm trying to cook up an equation that will give me position for a projectile which operates in the Newtonian Domain. So a the fall equation is: $$\mathbf{p_t} = \frac{\mathbf gt^2}{2} + ...
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How can one interaction influence the way another interaction generates mass?

This question arose as a follow-up of this one and applies generally to all interactions and all ways to generate mass. To make it clear, I take here the example of the neutron, whose mass is in ...
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Variation of the Einstein-Hilbert action in D dimensions without the Gibbons-Hawking-York term

Consider the standard Einstein-Hilbert action in $D \ne 2$ dimensions spacetimes : \begin{equation} S_{EH} = \frac{1}{2 \kappa} \int_{\Omega} R \; \sqrt{- g} \; d^D x, \end{equation} where $\Omega$ is ...
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Could gravity accelerate light? [duplicate]

Gravity causes anything with energy to accelerate toward the source. Black holes, for example, have such strong gravity that they pull in light and don't let any escape. But can acceleration still ...
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102 views

What general relativity predicts in such a situation?

If there's a system of a point mass or point particle with mass 'm' and a structure such that - The structure is made of many concentric spheres (shells) with certain thickness and the radius of those ...
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Effect of gravity on inhabitants floating in the Jupiter atmosphere

In several science fiction mythologies, humans live in artificial habitats in the Jovian atmosphere (Piers Anthony's "Bio of a Space Tyrant" and Ian M Banks "the Algebraist" for example). Assuming a ...
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111 views

Gravity amplifier

Just a hypothetical question. Is it possible to increase or amplify gravitational interactions between two or more bodies ( without changing the mass)? Will changing the graviton ...
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39 views

Analogy of curvature of space with sheet and ball [closed]

Many times people try to explain why mass curves the space with the ball on a sheet but in this analogy, I believe there is so many wrong corespondencies that it is actually a bad one. Implication ...
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“Warp-drive” thought experiment

Why wouldn't this "warp-drive" work? Assuming we can build a flywheel that can survive near light speed and have an onboard power storage or beamed energy that can spin it up to that speed and back ...
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Is a terminal gravitational center to the universe possible?

The current consensus is that there is no evidence of, or no way to tell whether or not there is a center to the universe. Considering our observable universe is only a small portion of what we know ...
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2answers
52 views

Using gravity's force to do work?

Since gravity is everywhere and we don't need to do anything to feel it and interact with gravity, can we somehow extract the gravity force to do work and power machines? For example, we've nuclear ...
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3answers
124 views

Why cant we harness gravity [closed]

We harness solar energy with constant supply of light but not with gravity. Why? What are the latest developments that can harness gravity? Why do Perpetual machines fail
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Can the force of Gravity be used to travel faster than light? [closed]

This question is just an idle curiosity of mine, but after reading the Honor Harrington novels, I was intrigued by the concept of using gravity to surpass light speed. Any thoughts?
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Largest item experiencing electromagnetic forces that are stronger than gravity

On the large scale, gravity is much stronger than electromagnetic force. But in what cases was the electromagnetic force stronger than gravity on the large scale i.e. objects of the size of the Earth, ...
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2answers
126 views

How to start an artificial gravity?

I understand how artificial gravity in space stations works. It is by normal force the wall exerts on the foot. But I wonder how to start it in the first place. I just learned about centrifugation ...
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3answers
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What is the smallest item for which gravity has been recorded or observed?

What is the smallest item for which gravity has been recorded or observed? By this, I mean the smallest object whose gravitational effect upon another object has been detected. (Many thanks to Daniel ...
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204 views

Why do we never account for the extra mass carried by a gravitationally excited object?

The mass of a bound system is the mass of its part minus the binding energy. For instance if you put an electron and a proton together to form a hydrogen atom you get a $13.6 \text{ eV}$ photon and ...
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54 views

Single photon's gravitational field: “where” is it?

When a photon passes through a hole in a screen, the photon's energy is pretty localized, namely a the hole. Now let the photon "fly" for a minute into the open void. The field representing ...
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How does the tension force of a massless string affect the speed of a mass on its end?

i,j, and k are the unit vectors in the following question, and $\omega$ is the angular velocity. Lets say you have a mass m attached to a mass-less string of length $L$ tied to a peg with no ...
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Gravity vs. Velocity time-dilation [duplicate]

Is there any difference in effects from time dilation of that due to gravity vs. that due to velocity?
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How does time stoppage inside a blackhole affect physics? [duplicate]

From the gravitational time dilation theory we know that at event horizon of a black hole the time should stop completely. However all the physics phenomenon we know (at macro level) e.g laws of ...
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What is the difference between gravitons and gravitational waves?

What is the difference between gravitons and gravitational waves? So as I understand, gravitational waves are predicted by and part of the theory of general relativity, whereas gravitons are predicted ...
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28 views

Is the curvature formed due to mass/volume of spactime convex or concave?

I am really confused about the curvature of space-time. Does it bends in a concave shape in presence of mass/volume as shown by the example of rubber sheet and ball or does it bends in a convex shape? ...
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Naked Singularity and AdS/CFT

I am a bit confused about the status of naked singularities that appear in black hole physics and more so in the context of AdS/CFT. Here is what I know about this in brief. For a charged ...
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1answer
58 views

Gravitational force and potential in infite slab

Let's say that we have an infinite slab of height $2h$ and mass density $\rho$. Let's define $x,y$ as the axis parallel to the slab and $z$ as the perpendicular one, with $z=0$ at the middle of the ...
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16 views

Weight difference on full moon and no moon day [duplicate]

Since Moon has an impact of gravity, would same piece of mass be heavier on a no moon day (since moon is at opposite side, thus pulling downwards) and lighter on full moon day (since the moon is at ...
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137 views

Confusion about gravity

I understand the “rubber sheet” model of Relativistic gravity is just an illustration, and beyond the initial issues of mixing three dimensional objects with a two dimensional representation of 3D ...
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82 views

Do things move towards each other in space?

I watched a video once explaining space-time curvature, and it said that one of the things that made Einstein think of it is because objects in free fall move radially inward, so two objects falling ...
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How general relativity shows that gravity decreases as we go inside the Earth [duplicate]

Why is it that gravity decreases as we go deeper inside Earth? Can anyone explain theoretically with reference to general relativity?
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Which is the mechanism through which dying stars shed their outer atmosphere and leave behind their core? [closed]

I was looking into neutron star creation and I read that when a star dies, it expells its outer atmosphere and leaves behind a really small really dense nucleus (a white dwarf if the first star was a ...
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Mass, density and gravity for 2D SPH

Having previously only worked with 3D sph, the 2d case is confusing me. The concept of mass and density as well as gravity is not easily converted, as I see it. As an example in 3D I take 1000 ...
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Why are Electromagnetism, Strong & Weak Nuclear and Gravitational Forces different?

If they are different then why the only thing that we 'see' in them, and that identifies them, the so called 'force' as we call and see it, is same among them all.
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Near horizon limit of near-extreamal black brane

It is known that the near horizon limit of a ($d+1$) dimensional extremal charged black hole (BH) is $AdS_2\times S^{d-1}$. I was looking at this paper by Faulkner et al. They consider a ($d+1$) ...
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If I throw an object from the roof of a high building, how does it fall? [closed]

Is it pulled towards the wall? And if so, what causes the pull?
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Accelerating Frame and Gravity

I have recently learned briefly that an accelerating frame is equivalent to a gravitational field in the equivalence principle. I'm sitting on a chair and I am experiencing the force of gravity and ...
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44 views

Why does the Gravitational Potential energy formula indicate that heavier masses in the same point in the field have lower potentials?

$$ U = -\frac{Gmm_E}{r} $$ Intuitively, it'd appear that the further away two objects are, the greater their gravitational potential, and this is confirmed by the gravitational potential formula. The ...
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Homework: Rope falling on scale [closed]

I think I have a solution for the following question, but it seems suspiciously simple to me: Suppose we have fixed a rope of Length $L$ and Mass $M$ at the ceiling such that the tip of the rope just ...
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1answer
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How to calculate the increase in temperature due to drop? [closed]

Question- Calculate the rise in temperature in celcius in a bucket of water after it is dropped from 50 m where acceleration due to gravity is 10. I know that I need to find the amount of energy ...
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If a metric has off diagonal terms, how can I calculate the tetrads?

If a metric has off diagonal terms, how can I calculate the tetrads? I need to calculate the Dirac gamma matrices in BTZ blackhole spacetime... $e^\mu_{(a)} e^\nu_{(b)} \eta^{ab} = g^{\mu\nu}$ ...
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1answer
54 views

Evidence of possible tidal effects close to a gravitational wave emitting system

Currently we are attempting to detect gravitational wave emissions using the LIGO gravitational wave detection system (and similiar systems), by attempting to detect very weak gravitational waves ...
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1answer
68 views

Questions about the velocity of the center of gravity

I have a physics test coming up in a couple of days and I really need to have some things explained to me. It is about something that I think is called in english "the velocity of the center of ...
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In a system of two charges, if one charge disappears, does the force on other charge vanish instantaneouly?

It is commonly asked that if the sun dissappears, will earth shoot off in a tangent instantaneously or after some time. We know from the theory of relativity that the gravity waves travel at the speed ...
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The distance between the two packages [closed]

A package is dropped form an airplane travelling horizontally at constant speed. Friction is negligible. One second later a second package is dropped. a) THe distance between the two packages will ...