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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3
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191 views

Do alternate theories for Dark Matter (like MOND) explain it's effect on gravitational lensing?

For a long time, I was sceptical about the evidence for dark matter. To me, it seemed like a pretty big leap to make when we have no idea whether or not our current models of gravity should apply ...
21
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2answers
810 views

How do spiral arms form?

Why aren't all spinning galaxies shaped as discs as my young mind would expect? I understand how the innermost parts of a galaxy spin faster than the outer parts, and that could explain why some ...
1
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1answer
162 views

Potential Energy of Springs and Gravity, and Work of a force

I am currently really stuck on this problem and I am not sure how to actually solve it, I think I can reason it out logically but I do not know how to show it. Here it is and under I will show what I ...
0
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1answer
41 views

Does Schwarzschild metric have cosmological horizon?

Since the space is not expanding in the Schwarzschild metric does that mean that there is no cosmological horizon? Also, what if the Schwarzschild metric was not asymptotically flat and we replace ...
0
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1answer
53 views

The EFE - The 'Mother' of all equations of motion in the universe?

This question addresses the scope of general relativity. Scientists and engineers solve all sorts of physical problems in all sorts of fields and often to solve these problems a 'system' is defined ...
1
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0answers
20 views

Are there any concrete data on the period of large amplitudes? To what extent are correction formulas useful?

Is there a site/pdf where I can find results of real and accurate experiments concerning the period of pendulums from 0 to 90°? (actual periods and not formulas). I once found one, but in spite of ...
11
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1answer
236 views

Equation derivation for skipping rocks

oWhy can rocks skip over water? For instance, if you conduct an experiment where you drop both rocks from the same height, but give one considerable acceleration in the x direction, one will fall in ...
2
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3answers
152 views

Gravitational potential in GR

In proving that the metric will play the role of gravitational potential, there is this chain of ideas: ...
2
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0answers
85 views

When spacetime expands to the point where galaxy clusters are not observable, will there by any interaction?

It's my understanding that in a few billion years, clusters of galaxies won't be able to directly observe one another due to the expansion of spacetime overcoming gravity between those clusters. ...
0
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2answers
30 views

Would a magnetic needle standing on it's point on a magnet be more stable than the same needle stood on a non-magnetic surface?

So I was watching MinutePhysics' video 'How long can you balance a pencil?' and it turned out to not be for very long. Would introducing a magnet to the equation make for different results? We can ...
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0answers
26 views

Motion on a rolling Body [on hold]

How can an object can continue to run on a rolling circle along the X direction and maintain a balance with specific acceleration.
-4
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0answers
34 views

How can the orbit of a planet having a 3600 year period and a perigee between Uranus and Neptune be computed [on hold]

There is a significant difference between the distance that gravity would move a planet with no velocity and the distance that gravity curves space time for a moving object. The 'fictitious' ...
0
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0answers
29 views

Variational principle conformal time in cosmology [on hold]

I am studying mimetic gravity in which physical metric is written as $$g_{\mu \nu}= \tilde g^{\alpha \beta}\partial_{\alpha}\phi\partial{\beta}\phi \tilde g_{\mu \nu}$$ The action of ...
14
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8answers
6k views

Is gravity just electromagnetic attraction?

Recently, I was pondering over the thought that is most of the elementary particles have intrinsic magnetism, then can gravity be just a weaker form of electromagnetic attraction? But decided the ...
-7
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0answers
27 views

what health per-captions should be taken for theoretical senerios [on hold]

so i been working on some detail research and i been having some difficulty applying perceptions since half of the experiment affects are only currently applying as theoretical phenomenons. but let me ...
1
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1answer
45 views

Meaning of “physical” and “gravitational” metrics

I've recently been reading some notes (following a paper by J.D. Bekenstein, titled "The Relation between Physical and Gravitational Geometry": http://arxiv.org/abs/gr-qc/9211017) on alternative ...
1
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0answers
89 views

Trebuchet launch into space

I was reading some questions on your site about using a Trebuchet to launch a payload into space. Would it be possible to use the same sort of principle, but to have, say a 100 mile steel cable ...
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0answers
29 views
2
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1answer
42 views

Shouldn't dark matter distort light and there for be directly detectable?

It is an established fact that gravity bends space time and therefore distorts light. We know that Dark matter acts gravitationally. So, just for giggles, lets say I had a sphere of dark matter ...
1
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2answers
43 views

Principle of equivalence

Einstein's principle of equivalence states that one can not distinguish between a freely falling nonrotating system in a gravitational field and a uniformly moving system in the absence of a ...
-5
votes
1answer
44 views

Difference between mass and weight [duplicate]

I already know that when I standing on weighing machine it's measuring my mass not my weight, but when I take the same machine to moon it's will read different value. According to my information that ...
0
votes
1answer
145 views

Certain doubts regarding the movie 'Interstellar' [on hold]

In the movie, or rather a scientific fiction, Interstellar, we saw in the last part, that the actor falls into the black hole, travels in time, which is a dimension inside the black hole, and then, ...
0
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0answers
63 views

A few questions about gravity [on hold]

Please don't count this as a duplicate, I have searched so many similar questions and have not found the answer. Also, don't count this as too broad because I can't find the answers anywhere else so ...
1
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1answer
43 views

Earth density distribution from shooting neutrinos?

I am interested in possibility of inferring Earth interior structure from gravitational data. As classical calculus problem shows, it is impossible to understand non-uniform density distribution ...
1
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1answer
143 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 ...
1
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3answers
81 views

Could black holes interact with dark matter at distances far greater than matter?

I watched this Nova episode on super massive black holes and learned that the speed at which the outer stars in a galaxy orbit correspond to the size of the black hole at the galaxy's center. They ...
0
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1answer
20 views

Would a fast moving (approaching $c$) stream of particles be affected by the gravitational pull of a gas giant?

I was inspired by this SE question. Would the gravitational field of a gas giant (such as Yavin IV) have an effect on the super laser (i.e. slow it down, change the direction), or is the mass so ...
10
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1answer
2k views

Why don't lakes have tides?

There's a tidal effect that we can clearly observe in oceans, which is the effect of gravity from the Sun and the Moon. If gravity affects everything equally, why don't lakes have tides?
2
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1answer
134 views

Physics of a cold and hot top

Imagine two tops made up of exactly one thousand atoms. One is kept at 4 degrees Kelvin, the other at room temperature. 1. Would they weigh the same given an arbitrarily precise scale in the Earth's ...
1
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2answers
62 views

Where to use acceleration due to gravity $g\propto\frac{1}{r^2}$

I (and we all) know that acceleration due to gravity $g\propto\frac{1}{r^2}$.Now my question is can I use this for depth.If not,why?If we can use it for depth or not struck me when I was trying to ...
0
votes
1answer
45 views

Gravity and centre of mass

Does gravity act entirely as if on the centre of mass? Often I have heard this, but it seems more realistic (even if less practical) if it acts on individual bits of matter, therefore weaker further ...
1
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2answers
67 views

Before we realized that supermassive black holes were at the center of large galaxies, how did the models explain galaxies?

So, I was watching this show on Netflix about supermassive black holes. I didn't realize that astronomers were surprised to find these black holes at the center of galaxies, because I cannot imagine ...
0
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0answers
29 views

How to calculate backreaction in AdS space?

This might be a very straight forward and basic question in GR. I am interested in calculating backreaction due to certain matter field (say, scalar) in AdS space. Should I put the energy-momentum ...
-1
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0answers
39 views

Why the Yang-Mills ansatz is able to describe every interaction we know? [on hold]

All interactions which seem to rule the microscopic world we have access to are described by the standard model, which is a Yang-Mills theory for the SU(2) x SU(3) x U(1) group. Also, gravity can be ...
4
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2answers
111 views

Gravity in 2d space and inverse linear law

In our three-dimensional universe, gravity obeys the inverse square law. In a four-dimensional universe, gravity would be expected to obey the inverse cube law et cetera. In a two-dimensional ...
0
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0answers
25 views

Expanding Electric Field, Magnetic Field in post-Newtonian Gravitational Potential

I've cross-posted this question from Mathematics since Physics is probably better suited for the nature of the question. I've ...
-3
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0answers
17 views

Controlling the flow of powder from a container, based on grams selected [closed]

was wondering how you would control the flow of powder from a container (with a small cylindrical dispenser at the bottom). The container is filled with powder. As the container drains, less ...
0
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0answers
16 views

Books on Spin-2 Gravity / Fierz-Pauli theory

I am trying to find a good pedagogical book/set of notes on Gravity as a spin-2 particle. I have been reading through Gravity & Strings by Ortin but it's very brief and offers little ...
2
votes
2answers
120 views

Lagrangian point or dark matter?

We know that spiral galaxies spin in a way such that we have to assume that dark matter is responsible for the extra mass required to do so. My question is, can Lagrangian points (L1 and L2) be used ...
39
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2answers
2k views

Are there tides in the atmosphere?

Analogous to the tides of Earths oceans, do the Moon and Sun cause our atmosphere to bulge in what could be described as a low and high tide?
-1
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0answers
63 views

Why are gravitational forces always attractive? [duplicate]

In my curiosity, gravitational forces, unlike electric forces, is always attractive, because of the empirical evidence. However, why is it so? In what model or theory can this phenomena be explained ...
0
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1answer
36 views

Gravitational intensity [closed]

I calculated the gravitational intensity and potential at a point P due to a horizontal linear mass distribution of length '$L$', mass '$M$' and uniform linear density at a distance '$R$' apart from ...
0
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1answer
54 views

Unruh radiation and conservation of energy

Consider the Minkowski spacetime filled by some fields in their Minkowskian vaccum state. Now consider a Rindler observer carrying with him, say, one liter of water. According to Unruh formula, the ...
2
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1answer
137 views

What causes gravity in M-Theory?

New and updated, because people were misunderstanding what I meant! General relativity describes gravity as the result of....(very roughly) spacetime curvature Newtonian gravity describes gravity as ...
5
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3answers
267 views

gravity delayed by speed of information transfer

A few months ago I had the pleasure of listening to an episode of RadioLab (a very informative podcast I would recommend to everyone) when they had Neil deGrasse Tyson on. He was discussing the very ...
1
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2answers
53 views

The pressure in a container of water is based on depth. So what happens if I remove the bottom of the container?

So I understand that if we have a system that involves a container of water the pressure will equal atmospheric pressure at the top and as we go further down the container the pressure will increase ...
2
votes
1answer
99 views

The ADM Energy of Gravitational Waves?

I have been looking for books about this question for several days. However, almost all books use Landau–Lifshitz pseudotensor to calculate the energy of Gravitational Waves.And they said the result ...
0
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2answers
111 views

Why does gravity affect time?

So Special Relativity states that for all non-accelerating objects of matter the laws of physics are the same. I'm confused on why this law of physic applies to objects in acceleration and gravity ...
3
votes
2answers
128 views

What are the photon/electron consequences of matter in a gravitational time dilation?

So I saw the movie Interstellar, and it got me thinking. I won't even mention all the plot holes, but I wanted to ask about a planet orbiting a black hole. I always thought you had to travel near the ...
1
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2answers
74 views

Why is sometimes more difficult to lift a baby?

I have a small cousin and she enjoys when I pick her up, which I can do pretty easily. Sometimes though she decides she wants to make my life difficult, and when she decides so, she tells me she is ...