Questions tagged [gravity]

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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Can something be a black hole in one frame of reference but not in another? [duplicate]

So my understanding is because E=mc^2, and kinetic energy is included in E, something moving quickly relative to you gains mass in your reference frame, compared to that same object at rest. Black ...
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Does Earth's rotation affect the orbital velocity of its satellites?

We all know about the spin of black holes. That spin and of course it's gravity determines the minimum distance a star can orbit the black hole with a min orbital velocity. Do we see similar result? ...
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How does gravity affect time dilation? [duplicate]

I understand that the faster you move through space the slower you move through time, but how does gravity play a role in that?
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How can time be curved?

Time isn't a physical object, but according to Einstein's theory of gravity, mass bends spacetime towards things with mass and makes them fall. How does a physical object affect something intangible?
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Normal force shift for ball kept in cavity

Adapted from JEE advanced paper-1 of 2020 If you see the left side of the Planck which the ball touches, it seems so that as we vary $\theta$, the contribution of the force from that point of contact ...
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Does dark matter act gravitationaly to itself. If Yes, why does not form more compact objects? [duplicate]

Does dark matter act gravitationaly to itself.If Yes, why does not form more compact objects? Can this be explained as its components have enough kinetic energy to overcome the collapse?
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Time dilation in free fall vs standing [duplicate]

A small object standing on a massive object undergoes time dilation relative to an observer far away that depends only on the masses and distance of the objects. What happens in the case of free fall? ...
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What is a charge, apart from fundamental property? [duplicate]

What really a charge is apart from saying its a fundamental quantity. I mean IF in case of gravity, its curvature of spacetime due to mass so just like that can anyone explain how charge like ...
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Conflicting intuitions about free fall

So I just started studying physics recently, and I came up with a question that I'm not sure how to solve, and I think it may be because of some fundamental misunderstanding. I don't want anyone to ...
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Why is gravity considered a force of nature? [duplicate]

Wouldn’t gravity be considered an effect to the other forces? An object of a given mass warps space time. The larger the mass, the greater the warpage. There is no graviton exchanged between the ...
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Earth as inertial reference frame: finite radius effects

In a recent question I tried to clarify under what conditions the Earth can be considered as an inertial reference frame. The opinions, summarized in my own answer to the cited question, are that ...
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I need help understanding Isaac Newton's Law of Universal Gravitation and Coulomb's Law [closed]

Do gravity or electrostatic forces have a distance limit ? When discussing Isaac Newton's Law of Universal Gravitation $F=\frac{Gm_1m_2}{r^2}$, I have heard many educated people say that because $r^2$ ...
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Loss of quantum coherence due to gravity [closed]

Consider a particle which moving inside a gravitational field.Will it lose its quantum coherence? According to GR , the particle will follow a geodesic but if it does then shouldn't its wavefunction ...
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Is there an approximate expression for the force between two black holes?

Just curious: is there an approximate expression for the gravitational attraction between two Schwarzschild black holes of masses $M$ and $m$, held without relative speed at some center to center ...
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Does an object rolling down a slope have more momentum than a object in free fall?

Physics newbie here. I am trying to figure out in which of the following scenarios would the object end up further from the starting point: Will a car that veers off a road that has a vertical cliff ...
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Does GR gravity obey a form of Gauss' law? [duplicate]

In Newtonian mechanics, Gauss' law is the assertion that, for any volume $V$ enclosed within a regular surface $\partial V$, the flux of the acceleration produced by gravity through $\partial V$ is ...
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Why can circular motion not be used to calculate kinetic energy of a person standing on Earth?

I did this question: In a sense we all have kinetic energy, even when we are standing still. The earth, with a radius of $6.37×10^6 \mathrm m$, rotates about its axis once a day. Ignoring the earth's ...
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Why and when can the Earth be considered an inertial reference frame?

The question has been asked (e.g., here and here), but I would like to get a more definitive and mathematically formal answer. The Earth rotates around its axis, around the Sun, and participates in ...
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How to interpret line of sight velocity distributions and dispersions of a galaxy?

What I did: I am analysing some simulation snapshots of the Milky Way and it is modelled as a DM halo – bulge – disc system. I produced some mean line of sight velocity (LOSV) and dispersion of mean ...
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Gravitationally-driven electrical potential differences in conductors

This question asks Free electrons in a metal are attracted by gravity towards Earth. So why don't they lay down to the bottom of the conduit, like sediment at the bottom of a river? The current ...
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If a black hole's mass is derived from its gravitational field, then why would mass be restricted inside the EH, while the field extends outside? [duplicate]

I have read this question: Let's consider the simplest kind of black hole, which is one with no rotation or electric charge. The quick answer to the question is "yes, the mass is entirely within ...
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If gravity isn’t a force how does it cause motion? [duplicate]

In general relativity, gravity is the effect of curving space-time caused by mass and is described as an acceleration. So what exactly is causing this pull towards the earth? Is a force not required ...
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Shouldn't black holes exert the same gravitational force as an object of similar mass but lower density?

If the earth got shrunk into the size of a peanut, it would turn into a black hole, which would have a higher density but same mass. Since the center of mass of both bodies would be the same, the ...
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If the exchange of virtual Gravitons isn't real why do bodies attract?

I have been told Earth is not really sending particles to me and keeping me on the ground. That it is just a convenient thing to do in calculations. However if the exchange of gravitons isn't real, ...
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If light and gravity travels in the same speed then why light cant escape the gravitational pull of black holes?

Speed of gravity is infinite? If fastest thing is light then how universe is spreading faster than the speed of light?
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When is gravity a force? [duplicate]

We all know that gravity is best explained by general relativity which says mass curves space-time. This means that gravity is not a force but an acceleration and we are “falling” towards massive ...
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Does Shape Dynamics use Space relationalism?

On Wikipedia it says Shape dynamics is an implementation of Space relationalism however I don't see how this can be true. In general relativity gravity exists thanks to Space substantivalism, the fact ...
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Is the Poincaré gauge theory a real gauge theory in the mathematical sense?

When studying Poincaré gauge theory using Milutin Blagojevich's book on "Gravitation and gauge symmetries" we find an interesting line of thought. But to get that I need to set some ...
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Yet Another Twin Paradox Question - Is orbit an inertial reference frame?

This question The "Satellite Paradox": Twin paradox in orbiting satellites asks something similar, but none of the answers quite get at the meat of what I'm trying to understand. On the ...
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Black holes and time dilation: how we could see interaction with other objects?

I have a question on the observable behavior of a Black Hole. So, I am not asking what is going on “now” at the Event Horizon or how can I “see” (get particles or waves). The question is how should it ...
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Is time dilation reduced when two opposing gravitational forces equally pull on an object? [duplicate]

(I apologize for my naivete in advance.) The Lagrange points around the earth and the moon provide a semi-stable space to put objects because the gravitational pull (combined with centripetal force) ...
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What is Shape dynamics?

From Wikipedia: In theoretical physics, shape dynamics is a theory of gravity that implements Mach's principle. In General relativity curvature of Spacetime causes gravity, in String theory it is ...
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If Graviton is considered as a particle, does Gravity have momentum?

Graviton is a hypothetical particle considered as a quanta of Gravity, if it is considered as a particle, does Gravity has momentum ?
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Why doesn't the curved spacetime curve the stick?

We know that gravity is not a force, but a curvature of the spacetime. This is a great visualization. But I don't understand something. If we live on Earth in a curved spacetime, and this curvature is ...
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What is the shape of an orbit with known period in the restricted three-body problem?

The three-body problem is the problem of taking the initial positions and velocities of three point masses and solving for their subsequent motion according to Newton's laws of motion and universal ...
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Black hole solutions to theories with no matter fields

The Schwarzschild black hole is described by a mass M but comes from the Einstein's field equations with the stress-energy tensor set to zero. If our theory does not include matter fields - say in the ...
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The hierarchy problem

I recently read a couple of scenarios to solve the hierarchy problem: the huge ratio between the electroweak scale $M_W$ of order $100-1000 $ GeV and the Planck scale $\sim 10^{19}$ GeV I think I ...
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Does electric field really exist or it is just an interpretation? [duplicate]

Did physicist create the concept of electric field to describe the interaction of charge particles at a distance? If they are real, do we have experimental evidence? Please describe some of them. And ...
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Is the entropy of a black hole relative?

I have a question about the entropy of black holes. Well, some time ago I was able to demonstrate theoretically that the entropy of black holes should be relative, that is, depend on the observer. But ...
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Energy of an object or a system?

We know that the gravitational potential energy of a system consisting of at least two bodies is given by $U=-\frac{Gm_1m_2}{r}$ where masses $m_1$ and $m_1$ are at a distance $r$ from each other. My ...
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Weyl tensor propagation equation and its practical use

There exists a differential equation for the divergence of the Weyl tensor, derived from the (contracted version of) differential Bianchi identity $R_{\mu\nu[\alpha\beta;\gamma]}=0$ and the ...
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Quantum gravity in an accelerated frame of reference

It is said that we can't study quantum gravity because gravity is a weak force. But gravity and acceleration are the same. Why can't we study quantum gravity in a strongly accelerated frame of ...
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How to amend General Relativity to include a position-dependent gravitational 'constant' $G$?

What is the best way to amend General Relativity to include a variable gravitational 'constant' $G$, that depends on the positions of all other masses? That is, if the amount of 'bending of space-time'...
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Does intrinsic curvature in a higher dimension mean that the lower dimensions also exhibit curvature?

If our universe has intrinsic curvature in a higher dimension, would that mean the 3 dimensions that we live in would be curved? and if so would the lower dimensions exhibit intrinsic or extrinsic ...
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Should the stars of a relativistic binary system have tangential acceleration?

Should the stars of a relativistic binary system have tangential acceleration?
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What is the true nature of gravity? [closed]

In 17th century, Sir Isaac Newton gave us the universal law of gravitation which stated that gravity is an inverse square force. In 1915, Albert Einstein recognised gravity as a curvature of space-...
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How would a weightless object behave on earth?

DISCLAIMER: Bear in mind that I am a mere 11th-grader: It came to me that an object with a net zero pounds (on earth) might sit more-or-less statically in the air. An example might be a ball of ...
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Behaviour of Fluids in Space [closed]

I would like to know about the effects of microgravity on fluids. This includes the changes in viscosity and the value of the Reynold's number with respect to the changes in gravity. I am struggling ...
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Can the spin connection defind on an orthonormal frame be non-metric compatible?

In the (holonomic) coordinate frame {$\partial_\mu$} with the affine connection $\Gamma^\alpha_{~\beta \gamma}$ and a generic metric $g_{\mu \nu}$, the manifold can acquire both torsion $T_{\alpha \...
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Could dark matter be made of particles that interact only gravitationally?

Are current observations consistent with the hypothesis that dark matter is entirely composed of one or more types of particles that interact only gravitationally with each other and the usual matter? ...

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