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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Energy conversation of Virtual Particles - Quantum Fluctuation?

I (as a middle-school student) was wondering how virtual particles even conserve energy of the entire system? I don't mean the particles energy, but its conservation of surroundings? Let me explain ...
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36 views

Can Newton's Law of gravity be deduced using dimensional analysis?

I tried using dimensional analysis to deduce Newton's law of gravity but I wasn't able to do so as one of the equations were $0=-2$ which is a contradiction. But I thought that we can't do that ...
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97 views

How can Terminal Velocity be greater than gravity? [on hold]

It's been over a decade since my last high school physics class, so I apologize in advance if this is a dumb/ignorant question, but how can a skydiver fall faster than the speed of gravity? If gravity ...
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4answers
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How fast would someone have to run to travel vertically up a wall?

I am currently doing a physics project on the effects of so-called 'super-speed'.I was wondering how fast you would have to run to vertically travel up a wall? That is, to negate the force of gravity. ...
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What is the speed of times arrow [on hold]

If the maximum speed of time in a vacuum is C you would have included time in relativity theory and have a definition of space time, Or the mass-time equivalence. A thought experiment.
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1answer
37 views

Why does gravity enact force? [on hold]

Gravity would cause two objects in a vacuum to move toward each other. I understand that gravity is a force that exists as a product of energy's original conversion into mass and the continuing change ...
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39 views

Does entropy increases due to gravity? [on hold]

Imagine travelling to the surface of a neutron star where the very intense gravity would make you weigh 140 trillion times more than we do on earth. It's enough to significantly raise the entropy of ...
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0answers
37 views

Temperature in CFT

Non-vanishing Temperature can break conformal symmetry(Can anyone show this point explicitly), my question is that in AdS/CFT the temperature of boundary field theory is non-zero, why the boundary ...
3
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1answer
371 views

How quickly does gravity extend from created mass? [duplicate]

I apologize in advance if this is a stupid or off-topic question. Since Energy can be converted into matter according to $E=mc^2$, how fast does it take for the gravity of that new matter to extend ...
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27 views

Calculating time of being in a lift only by weight & travel distance

If someone is in a lift and normally weighs 90kg, when the lift starts accelerating the person weighs 100kg. After the lift has maintained a constant speed for a while it starts slowing down. While ...
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1answer
50 views

Increasing matter density in the Friedman equations?

From what I understand, the Friedman equation is $H^2=\frac{8\pi G}{3} \rho$ and the $H$, the Hubble constant, is a measure of the rate of expansion of the universe. What I am confused about is that ...
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39 views

Self-replication of gravitons in string theory [closed]

How does the self-replication of gravitons work? Edit: Red Act says that prof. Luboš Motl could have meant self-interaction and not self-replication.
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555 views

Why heavy elements don't sink to the core?

If earth assembled out of space dust, how come we find heavy elements like gold, silver, uranium and bunch of others that are heavier than iron on the surface? I mean silicon (Si mass 28.084) being ...
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1answer
34 views

Cluster of Black Holes around a Central Point [duplicate]

Within the Star Wars Extended Universe, there is a science base on a small object within a near impenetrable sphere of Black Holes. These Black Holes remain in roughly the same position and, according ...
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2answers
60 views

Conservative force as a potencial energy gradient

A conservative force $\vec{F}$ is apparently defined as the gradient of a potential energy $U$: $$\vec{F} = -\nabla\ U$$ I am curious if this definition was originally used to describe a ...
2
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1answer
48 views

Does velocity determine a geodesic?

If the gravity effect we witness is due to objects travelling along geodesics, why is the geodesic different for objects with different velocities if there is no gravitational force as such? For ...
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0answers
34 views

Geometrised Units

I am curious as to how to express a area units in geometrised ones. I was reading on wikipedia and saw that when angular momentum is converted into geometrised units, it is expressed as a dimension of ...
7
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1answer
89 views

Why is it so coincident that Palatini variation of Einstein-Hilbert action will obtain an equation that connection is Levi-Civita connection?

There are two ways to do the variation of Einstein-Hilbert action. First one is Einstein formalism which takes only metric independent. After variation of action, we get the Einstein field equation. ...
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1answer
105 views

Advanced Gravitational Waves? [closed]

Do advanced gravitational waves exist?
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4answers
124 views

When does acceleration due to gravity equal positive/negative? [closed]

For example a projectile is launched at an angle. What would $a$ in $y=vt +.5at^2$ be? Let's say I choose up to be positive. How do you not confuse yourself whether to use positive or negative $a$?
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1answer
42 views

Effect of gravity on large tower with reduced air pressure

Suppose I built a 5km high building. The pressure of the air at the top would be around 50% compared to the pressure at the ground (I assume that the exact values don't matter in my case). Now ...
0
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1answer
39 views

Confused about equations for the Big Bang in general relativity ad loop quantum gravity?

I am trying to get a vague understanding of the mathematical equations for the Big Bang in GR and LQG. My understanding so far is that when the universe is assumed to be homogeneous and isotropic, ...
10
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1answer
1k views

Does light lose energy in transit?

Consider a photon is an energetic particle and therefore has a gravitational field. When a photon passes a molecule or particle of dust in space it will pull the dust towards it and deform the dust. ...
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3answers
2k views

Does Gravity Really Exist? [closed]

As far as I understand some of the readings, Gravity does not exist in real terms. It's only a way of modeling motion as we see. Einstein for example explained the motion without having to have ...
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0answers
60 views

Calculating PSI generated by water entraining air as it flows down a pipe

This is the concept used in a trompe. Basically, the idea is that if we allow water to flow down a pipe and if that pipe has inclined air intake orifices near the top where the water enters, then the ...
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1answer
77 views

Does Liquid Immersion protect against G forces?

I'm under the impression that if an object is immersed in water it can be protected from the effects of Gravity - or in other terms appear to be in a 0G enviroment. Typical examples of this include ...
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2answers
53 views

What happen to a spoon which is detached from the satellite?

Suppose a spoon is a part of satellite but after detachment from the satellite Does it fall to the ground straight or does is take a parabolic path or any other path before coming to the surface of ...
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100 views

What is the cause of gravitional force of attraction?

Ok,this is a silly question. But for quite long I have been thinking about this. What is gravitation all about?? My book directly writes since force of gravitation is directly proportional to the ...
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1answer
83 views

Modifying Newtonian gravity to fit observed precession of Mercury's orbit

The idea is to modify Newtonian gravity so that it fits measurements of orbits around the sun. For example the precession of Mercury's orbit unlike Newtonian $n$-body simulations. I'm currently not ...
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2answers
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1answer
2k views

If a photon goes up, does it come down?

If light can be bent by gravity, does a mass as dense as a star pull any fraction of photons back towards itself?
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41 views

What is the status of gauged gravity [duplicate]

The Standard Model of elementary particles is a gauge theory with gauge group $SU(3)\times SU(2)\times U(1)$, which is really a successful theory. We might be able to quantize gravity similarly. ...
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3answers
889 views

Has the gravitational interaction of antimatter ever been examined experimentally?

I know that the gravitational interaction of antimatter is expected to be the same as normal matter. But my question is, has it ever been experimentally validated? I think it would not be a trivial ...
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0answers
50 views

What's the meaning when Kerr-Newman metric's mass is zero?

Kerr-Newman metric represents the spacetime of a charged and rotating black hole. If the mass parameter is zero, this metric is still not the Minkowski spacetime. What's the meaning of a charged and ...
2
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2answers
74 views

Stability of planet-enclosing shell supported by atmosphere

I understand that a hollow spherical shell of uniform density gives net zero gravitational attraction to objects inside it. So in vacuum, a ball at the centre of a spherical shell would not be stable ...
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1answer
66 views

Can an analog to the Meissner Effect be proposed for matter and gravitational fields?

In the study of electromagnetic fields and quantum electrodynamics we observe and theorize on the behavior of superconductivity and the Meissner effect. Has an analog of these behaviors been proposed ...
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131 views

Does accelerating generate gravitons?

If gravity and acceleration are indistinguishable, then does that mean converting potential energy to kinetic energy generates gravitons... but only temporarily until you stop accelerating?
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1answer
25 views

Distance as a function of time where acceleration changes with respect to distance

I was thinking the other day about gravity. I know that acceleration in a magnetic field changes with respect to distance from the center of the field. So I was thinking, how would one find the total ...
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1answer
32 views

Weighing with One-Foot Scale

I stand with left foot on a scale and the other on a piece of effectively incompressible material at the same initial height at the scale's top surface. The weight shown is WL. I repeat with right ...
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3answers
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Can mass be directly measured without measuring its weight?

From Wikipedia, http://en.wikipedia.org/wiki/Mass Inertial mass measures an object's resistance to being accelerated by a force (represented by the relationship F=ma). Active gravitational ...
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1answer
44 views

Would an ideal gas be colder at higher altitude due to gravity?

Since gas molecules are affected by gravity, wouldn't that make gas molecules at higher than average elevation slower (at the top of their ballistic parabola) and thus colder than air molecules ...
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3answers
86 views

How come we talk about gravitational potential energy and not gravitational potential?

With regards to gravity the equation learned is $$U=-\frac{GMm}{r}$$ And the relationship to force is $$F=-\frac{dU}{dr}$$ In electrostatics we instead talk about electric field and electric ...
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1answer
72 views

How does gravity's space time distortion access energy to induce freefall? [closed]

An observer, standing on top of a building, has a gravity switch (use your imagination) which allows him to turn gravity on and off. He turns the switch off, then releases a pool ball over the edge ...
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3answers
110 views

Is the Moon freely falling towards the Earth?

The Moon is revolving around the Earth and its centripetal acceleration is towards the Earth. Does it mean that the Moon is freely falling towards Earth? What is the cause of the Moon orbiting around ...
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1answer
63 views

Is there, and if there is, what is the name of the concept that matter is made out of void/space?

I can't recall where I heard about this, but it was rather intriguing. I recall the notion that matter is compressed void/space, where I remember an example of a bedsheet representing space, and the ...
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0answers
42 views

Finding equation for acceleration using mass1, mass2, gravity, theta, and Mu [closed]

So, the only question I could not solve in this chapter for AP Physics, and I really want to understand it. We have a situation like this: There is a box sitting on an incline. We are trying to ...
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2answers
51 views

Does the distance two weights are from you alter the difficulty of lifting them?

If I am weightlifting and I choose to do the deadlift, does it matter how far away from me the weights are on the bar, given that they are equally distance from me on both sides. E.g. I am deadlifting ...
2
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3answers
68 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? ...
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0answers
31 views

How big could a bubble of air and water be in zero gravity? Assume air surrounds and fills a bubble of water

I am designing an all water planetoid for a new science fiction novel I am writing. The Planetoid is a spherical bubble of water filled with air, and covered by a sufficiently thick atmosphere to ...
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1answer
40 views

Expansion of the universe [closed]

If matter cannot be created nor destroyed, I would assume that the universe expands only to the point that energy is expressed from the objects inside it until it collapses onto itself, given as the ...