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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Why is gravity weak at the quantum level?

Why is gravity stronger than other forces at the macroscopic level, yet weaker than other forces at the quantum level? Is there an explanation?
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What would be the optimal weight of a ball if I want to throw it as far as possibile?

Assume the force behind my throw to be X. Assume the point of release is 2 meters above ground. Asume the ball is made of shiny steel. I'm not sure if the material matters, I'm just thinking that ...
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Voyager local time dilation (caused by gravity)

Voyager I, as an example, taking account gravity and setting aside effects of speed as cause of time dilation. If it is very far away from earth and sun, so then there must be a difference in the ...
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Gravothermal catastrophe: looking for simple explanation

I am beginning to try to understand the gravothermal catastrophe. I was hoping someone could provide an explanation to help me understand what the gravothermal catastrophe is and why it is important, ...
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gravitational force and irreversibility

If we place a ball at a certain height it falls and the process is irreversible. Is there any entropy change associated with the falling of ball? If so why?
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If gravity dropped off with the cube of distance

If gravity, for instance, dropped off with the cube instead of the square of distance from the Sun, would the planets still follow elliptical paths?
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Shouldn't dark matter distort light and therefore 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 ...
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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 ...
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Frame dragging — is there a “non-tiny” example?

Now. As I understand it, in fact, the earth (10^25 kg) creates a very small, very tiny, frame dragging effect. Indeed, we have measured this using satellite experiments. So, the Earth (10^25 kg) ...
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What's wrong with my calculation of gravitational potential for a uniform sphere?

This is really embarrassing, but I'm not quite sure where I'm going wrong here... Why is this calculation of the gravitational potential inside a sphere with uniform mass distribution incorrect? ...
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Why meet at the center of mass?

If two objects of different masses are held at a distance $d$ and then I let them go, they will meet at the center of mass of the particle system due to mutual gravitational attraction My question ...
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Why isn't all of the dust in a nebula used in the formation of a star?

I was watching a show on discovery and according to it, in a nebula the dust and gases slowly come together and as the gravity increases and the pressure rises in the core the gases fuse together and ...
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What kind of energy gravitates, and why?

When listing energies for the purposes of keeping track of conservation, or when writing down a Laplacian for a given system, we blithely intermix mass-energy, kinetic energy and potential energy; ...
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Can Vesta dominate the orbits of other asteroids?

I think I remember a talk where a professor said that Vesta is a particularly important asteroid because its gravity is strong enough to perturb other asteroids. In spite of Vesta's size, this effect ...
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Wavelength of photon changes as it rises from a planet's surface(acc. to this equation)?

The setup assumes a large mass(Earth?) an a photon launched from its surface initially. The wavelength of the photon on launch is known. Then the new energy of the photon is compared with energy it ...
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Do all atoms in the universe gravitate each other?

I understand that matter will gravitate toward matter. (ex: Earth gravitates a satellite toward it, and the satellite toward Earth.) Does this always apply, regardless of distance?  Take two atoms, ...
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Strongest force in nature

Possible Duplicate: What does it mean to say “Gravity is the weakest of the forces”? It is said nuclear force is the strongest force in nature.. But it is not true near a black ...
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Planet orbits: what's the difference between gravity and centripetal force?

My physics teacher says that centripetal force is caused by gravity. I'm not entirely sure how this works? How can force cause another in space (ie where there's nothing). My astronomy teacher says ...
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Can an observer know what is the source of gravity?

There's an observer in a closed room without windows under an influence of gravity force. Can he determine what is the source of gravity - whether it's a spinning motion, acceleration or huge mass ...
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Square root of a matrix appears in massive gravity. How to solve $\sqrt{A+B}$ perturbatively

$A=\text{diag}\{\lambda_1,...,\lambda_n\}$, where $\lambda_i$ can be any number and not necessarily a small number, $\lambda_i>0$, $B$ is a positive definite symmetric matrix, and ...
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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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Antineutron repelled by gravity?

I was reading an old post, Can gravity be shielded, like electromagnetism?. One of the responses had this comment. There are some experiments trying to measure whether antiprotons ( antimatter) ...
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The original thorium reactor?

With lunar thorium being common, and heavier than iron or nickel, does earth's core have the the occasional nuclear reaction?
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What made Einstein think that gravity was caused by the curvature of spacetime?

What observation/thought experiment led him to think this?
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Why does unequal mass distribution cause orbital decay?

It's well known that in low orbits around astronomical bodies with uneven mass distribution, orbits will shift around, and the orbiting object may crash into the surface. Why is this the case? ...
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What predictions can a quantum gravity theory make?

Some of the major challenges that heralded the need for quantum mechanics we're explaining the photo-electric effect, the double-slit experiment, and electrons behavior in semi conductors. What are ...
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Any simple reason why spin 2 polarization tensor should be symmetric in $\mu\nu$?

Perhaps this is obvious to the not so tired one, but is there any reason why the five spin 2 polarization tensors $\epsilon_{\mu\nu}^{a}, a=1,\dots,5$ should be symmetric in $\mu\nu$? While I'm at ...
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What is the reasoning behind the Hill Sphere?

According to Wikipedia, Hill Sphere is : the volume of space around an object where the gravity of that object dominates over the gravity of a more massive but distant object around which the first ...
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Why does mini quadcopter doesn't maintain altitude?

I have a mini quadcopter controlled by remote controller. I have set the motors (e.g 50% thrust) it will remain at altitude at 10 cm~ but once I increase to 80% and then follow by decrease to 50% I ...
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What would be the effect on gravity if space expanded at > $c$?

If space were to expand at > $c$ (as in inflation) would that mean gravity would no longer have any effect on the curvature of space, since gravity can only propagate at $c$?
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Relation between the determinants of metric tensors

Recently I have started to study the classical theory of gravity. In Landau, Classical Theory of Field, paragraph 84 ("Distances and time intervals") , it is written We also state that the ...
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Can a black hole collapse in itself?

As we know that the black hole is a lump of highly dense matter, and that's the reason for it's so strong gravitational force. Bat let us assume that it has sucked up a huge amount of mass and it's ...
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Impact of gravity on bone structure [closed]

Some suggest that if a human was born and raised in a gravity-less environment their bone structure/strength would be different that for children born on earth. If this is the case do you think this ...
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Gravititonal fields compared to electromagnetic fields - are they infinite in range?

me and my friend has a discussion last night, and he argued that both an electromagnetic field and gravititonal field are infinite in their area of effect, but with diminishing effects as you get ...
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Can I calculate the height of a cliff from weight of falling object and time taken?

I'm sure a simple question. I have a video of me jumping off a cliff into a river. I want to calculate how high it is. I know my weight, acceleration due to gravity of course, and I can get the ...
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Is curvature space-time has impact on the object geometry

When we have e.g. metallic cube of dimensions 1x1x1m and we put it on the space without gravitational force the cube has equal 1x1x1m and we can use Euclidean geometry. But when this cube move on ...
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Does the existence (now proved) of gravitational waves imply the existence of Gravitons?

I studied the theoretical part about the Gravitational waves in General Relativity (linearization of gravity and small perturbations of the metric and so on). But I was wondering about: since ...
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Gases Expanding and Bonding in the Vacuum? Frozen Clouds

Why do gasses expand in space rather than attract forming a liquid? Do some gasses attract or bond when they get colder and what would be the characteristics of it in space? Would it be like powder ...
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Detection limits on 'd' if gravity force was proportional to $1 / (R+d)^2$

Assume the force of gravity is proportional to $1/(R+d)^2$ where $d$ is sufficiently small, then, how small would $d$ have to be to evade detection by modern experiments? My thinking is that if $d$ ...
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How does a boomerang behave in microgravity?

Let's say I have perfected a boomerang throwing machine - in Earth surface conditions the boomerang is always thrown the same way, and always returns to the throwing arm. And let's say I've sponsored ...
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How many tons of lead is needed to curve space 1 nanometer? [closed]

How many tons of lead is needed to curve space 1 nanometer?
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gravitational wave detection using interferometer detectors

I understood that the basic idea of the interferometric detectors is the michelson interferometer experiment, in which the change in the position of the mirrors will cause the interferometer ( ...
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What would happen to a star if a Dyson sphere lined with mirrors reflected a significant portion of the stars light back to the star

I have looked for similar questions here on stack exchange. The closest example to this that I found is Could a Dyson sphere destroy a star. That question assumed less than perfect absorption of ...
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Wouldn't dark matter throw off the calculation of Earth's 'light' mass and estimates of its composition?

The Cavendish experiment first determined the mass of the Earth and (arguably) the gravitational constant. However, given the ubiquitous nature of dark matter, it seems reasonable that at least some ...
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Does uniform distribution of background matter affect the dynamics of a gravitational system?

Situation 1: A test particle of mass m moves around a big mass M in a Keplerian orbit. The orbital period is easily found, given certain initial conditions. Situation 2: The same system of two bodies ...
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Electromagnetic radiation bending on Earth

Most articles say that a radiowave is able to propagate itself beyond the horizon because it is reflected off by the ionosphere (and the Earth itself). But do radio waves also get bent according to ...
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Could fish in plastic bags filled with water float like that?

I saw this gif earlier and it bothered me how the plastic water bags with fish in it are not submerged in water like they would if we don't do anything special with the water inside and outside the ...
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How to explain centripetal force in terms or relativity

At the end of a video of dropping a ball and feathers in a vacuum, Brian Cox explains that the Ball and Feathers, as understood in terms of General Relativity, aren't falling. (apologies I can only ...
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How is sweating a pipe an example of capillary action?

I learned how to sweat a pipe today from my father. If you're not familiar with the process, this might help. One thing that jumps out at me is this line (from the above link, as well as my father's ...
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Minimal vs. Non-minimal coupling in General Relativity

What is the difference between Minimal vs. Non-minimal coupling in General Relativity? A brief introduction to Minimal Coupling in General Relativity could be useful too.