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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6answers
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The square in the Newton's law of universal gravitation is really a square?

When I was in the university (in the late 90s, circa 1995) I was told there had been research investigating the $2$ (the square of distance) in the Newton's law of universal gravitation. ...
2
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1answer
94 views

Could gravity be repulsive at short distances?

I was wondering if it would be consistent with empirical data if gravity became extremely repulsive at short distances. For example (please bear with my use of classical formulas, I know little of ...
0
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2answers
107 views

Why is the potential energy for a body raised up by a height negative?

I tried deriving the potential energy of a body when raised at a height $h$ above the earths surface, using the formula: $$PE = -W_\text{conservative}$$ where $W_\text{conservative}$ is the work ...
2
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1answer
76 views

Why doesn't the light get out?

You're standing on a gedanken planet holding a laser pointer straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now I wave my magic gedanken ...
3
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2answers
675 views

Special relativity paradox and gravitation/acceleration equivalence

One of the features of the black hole complementarity is the following : According to an external observer, the infinite time dilation at the horizon itself makes it appear as if it takes an ...
0
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0answers
20 views

Anti-Gravity or Gravity Levitation or Gravity Manipulation Propulsion [on hold]

Why mankind has not leaped (or publicly acknowledged) much on anti gravity propulsion research ? I have read (seen in documentary as well) about Nazi's research about Bell shaped anti-gravity ...
5
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2answers
62 views

Would the presence of B-modes in the CMB provide evidence for quantum gravity?

Finding B-modes in the CMB (which aren't due to foreground contamination) would be evidence for gravitational waves, because they cannot be produced by density perturbations (to first order, is my ...
0
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1answer
70 views

Is possible to generate energy from gravity?

When the wind goes through the vanes of an wind turbine, it's generate energy. When the water goes through the water turbines, it's generate energy. So my question is short and simple, is possible ...
4
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4answers
1k views

How long would it take to travel through a wormhole?

Assuming wormholes exist and you put some matter into one, how long would it take to reach the other end versus how far apart the two ends are? Basically, by how much does a wormhole stretch ...
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0answers
80 views

how does gravity exist?explain in detail about the factors responsible for it? [on hold]

If gravity really exists,then, what are the basic factors that are responsible for it's existence?...i have some supporting statements to contradict the existance of gravity...and i have added my ...
4
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2answers
114 views

Why do clusters of stars eventually dissipate?

Why don't the stars in a star cluster attract each other gravitationally, forming one big star? What causes a cluster to disperse the stars in it?
1
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2answers
44 views

Gravitoelectromagnetism higher-order effects

See http://en.wikipedia.org/wiki/Gravitoelectromagnetism#Higher-order_effects According to the Higher-order effects... "Gravitomagnetic arguments also predict that a flexible or fluid toroidal mass ...
0
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0answers
64 views

If I am in an elevator, with a weight of 120, and I am descending at 8 m/s, what is my apparent weight? [on hold]

Suppose your weight is 120 lb. You are riding in an elevator in the Sears Tower while standing on a bathrooms scale and watching readings. Imagine that the elevator keeps descending at a constant ...
0
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0answers
22 views

Force of gravity exerted by/on Earth/Sun in a given coordinate system - not sure about the question [on hold]

I have a question: At a certain time in a coordinate system, the Sun is at the origin and the Earth is at position angle 225 degrees. What is the force of the Sun on the Earth? What is the force ...
2
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4answers
154 views

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? ...
0
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1answer
55 views

Will boomerang work in vacuum chamber on Earth?

Earth's gravity, the way we spin and air pressure are essential to have fun with the boomerang. Suppose we do same thing except in a vacuum chamber totally devoid of air will it still be able to ...
0
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2answers
86 views

Is there any way gravity can reflect light?

I know gravity leads to certain interesting optical phenomenon. I know light curves around a massive body, I know light red shifts if we look far enough in space. Is there any configuration that could ...
0
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0answers
16 views

how to make an equal-arm balance beam?

Use an equal-arm balance beam, with a 250 kg counterweight suspended 5 cm in the air on one end, and the mass to be moved just touching the ground on the other end. Energy storage is in gravitational ...
0
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1answer
44 views

Similar effect to gravity horizontally? [on hold]

I've been pondering this today. Say you have a moving vehicle, with enough space to move around in (say, an empty moving truck). How fast would it have to be going for you to jump and go flying across ...
0
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1answer
75 views

If I launch a coin, will it always fall down?

I was running in the university aisle (I was late for the statistics lesson) when I heard: "In normal condition there is a possiblity that if you launch a coin instead of falling down it'll go up". Is ...
0
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0answers
39 views

If the great pyramid was built in 20 yrs for Khufu, what forces were used for its building? [on hold]

If the great pyramid was built in 20 yrs as they claim, this means that every 2.3 minutes a stone as heavy as a car was quarried, moved 500 miles up the nile river shaped, hoisted and set. This would ...
0
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1answer
66 views

What it would look like to observe people with a different time flows?

As I learned, that the bigger gravity source you are influenced by the more slow time ticks for you, the farther away you are from a gravity source the faster times ticks. So Imagine two different ...
1
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2answers
6k views

Would a light or a heavy ball roll fastest down a slope?

A small, light ball and a larger, heavier ball are released from the top of a slope. Which will move further? which will come down faster?
1
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1answer
112 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 ...
5
votes
4answers
713 views

Gravitational lensing or cloud refraction?

My current understanding of gravitational lensing follows When a star or other massive body passes between us and another star, the phenomenon generally labeled 'gravitational lensing' occurs. The ...
1
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3answers
1k views

Aircraft Level Flight Trajectory

An aircraft climbs to 15000 feet and enters 'level flight' phase. My basic knowledge of physics says that forces on the aircraft at this time are balanced - as seen in this diagram. Would an ...
1
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1answer
68 views

Study the center and interior of a black hole using quantum entanglement

Having just watched the latest in a long line of space movies; Interstellar tries to combat the problem of studying the center of a black hole and understanding what's going on inside. My question is, ...
4
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2answers
59 views

How is the conservation of momentum satisfied in long-range attraction such as electromagnetism and gravity?

I'm not a physicist, but my understanding is that electromagnetism (including attraction between opposite charges) is mediated by the photon, and gravity is probably (hypothetized to be?) mediated by ...
0
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0answers
39 views

Does Gravity Act on Any and All Things in the Universe? [duplicate]

I'm studying physics, and the questions below popped up in my head. I learned that all objects on planet Earth fall due to the influence of gravity. A ball falls. A mug cup falls. A coin falls. ...
0
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2answers
73 views

Acceleration to lightspeed using gravity

Suppose we have a very advanced spaceship that (aside from colliding with planets or entering a blackhole) is indestructable, and can go very fast, but is incapable of moving at lightspeed on it's ...
5
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1answer
104 views

What causes light to travel through a curved fountain of water?

Today I observed a tilted fountain spurting water upward (the water fell smoothly; no detectable turbulence). A colored light was shown upward into the water as it left its source. This light traveled ...
0
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1answer
35 views

What observation(s)--if any--confirm that the types & concentrations of energy, which are influenced by gravity, are the same ones that cause gravity?

General relativity allows various forms of energy to participate in the gravitational force. What observation(s)--if any--confirm general relativity's notion that the various types & ...
1
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1answer
57 views

Real-world evidence that non-massive entities (or even: antiparticles), and their behaviors, are sources of gravity?

The theory of general relativity tells us that non-massive entities, and their behaviors, are possible sources of gravity. Mass isn't needed, the theory says. What's the real-world evidence that ...
3
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2answers
52 views

2 different density liquids in space

Lets say you are in deep space with basically zero gravity. You have a ball of water floating in front of you. If you carefully injected that ball with a syringe filled with vegetable oil, what ...
1
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1answer
123 views

Gravity in $d$ spacetime dimensions

Given the following action $$S=\frac{1}{16\pi G}\int d^4x \sqrt {-g}(R+aR^2+bR_{\mu\nu}R^{\mu\nu}+cR_{\mu\nu\lambda\sigma}R^{\mu\nu\lambda\sigma}),$$ which is in 4D. How to we generalise this ...
2
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0answers
55 views

What are Galileons good for?

Lately I've seen many papers on types of field theories known as Galileons, and I'm wondering what the motivation for studying them is. I often hear of them in the context of "well-behaved" IR ...
39
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8answers
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In theory, could gravitational waves be used to make a “gravity laser”?

The sources I've read compare gravitational waves to electromagnetic waves. I'm curious to what extent this is. In theory, could gravity be harnessed in similar ways to how we've used electromagnetic ...
-2
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1answer
127 views

Thought experiment on graviton breaking the speed of light [closed]

The effect of gravity travels at the speed of light. Suppose we can entangle a pair of gravitons (which are only theoretical, but who knows for sure?) and separate them over a vast distance. Hold on - ...
2
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1answer
231 views

Will a hot object have more gravity than a cold object?

Imagine two objects, identical and having the same mass. Now my question is, if you heat one object and do not do anything with the other object, will the hot object possess more gravity (because it ...
2
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5answers
131 views

A ball in the gravity potential field of a black hole — seems a paradox

As illustrated in the following diagram (A, B, C, D are 4 specified space points, and C is close to a black hole), a small ball at distance of a black hole is stationary (suppose now it's mass is m0) ...
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4answers
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Will an object always fall at an infinite speed in a black hole?

Most of you if not everybody will agree that the stronger the gravitational pull, the faster an object will fall. For example, on a planet with 50 times the gravity of Earth, any object will hit the ...
2
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1answer
62 views

Heuristics for the Hawking mass

I have the following definition of Hawking Mass. Given a spacelike 2-surface $S$ embedded in a 3+1-dimensional Lorentzian Manifold $L$, $$ M(S) := \sqrt{ \frac{\text{Area}(S)}{16 \pi}} \left(1- \frac ...
2
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1answer
86 views

Can energy bend space? [duplicate]

I know mass bends the space around it and I also remember matter can be converted into energy and vice versa, so my question is: can energy interact with space in a similar fashion as matter does?
2
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3answers
170 views

Einsteins gravity Space time

I'm having a difficulty in understanding Einstein's version of gravity as "space time curvature" (I could be a total physics idiot, please point out !). How does an object on the surface of earth ...
0
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1answer
31 views

How to prove that the nonlinear completion of free massless spin-2 action must be Einstein-Hilbert action?

There is a saying that the nonlinear completion of free massless spin-2 action in Minkovski spacetime (that is Fierz-Pauli action) must be Einstein-Hilbert action up to Lovelock invariants. I find a ...
2
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1answer
33 views

Deriving the Fierz-Pauli propagator

Fierz-Pauli action can be written as $$ S = \int d^Dx \; \frac{1}{2} h_{\mu \nu} \mathcal{O}^{\mu \nu, \alpha \beta}h_{\alpha \beta} $$ where the operator $$ \mathcal{O}^{\mu \nu} {}_{\alpha ...
2
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1answer
57 views

Non-linearity and self-coupling of gravity

I have heard that non-linearity of Einstein's field equations has to do with the fact that gravity self-couples. What does non-linearity have to do with self-coupling?
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4answers
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A cup of water in ZERO gravity

What will happen if I try to pour a cup of water in zero gravity, into another empty cup? Will the water come out of the cup? The adhesive force between the water molecules and the interior of the cup ...
2
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1answer
52 views

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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3answers
61 views

Why does weight affect acceleration with gravity

I'm sure this question has been asked before, but my question is different, because it can't be answered with some formulae. My question is, why do heavier objects decelerate faster when moving away ...