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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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 ...
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667 views

String theory and trace anomaly in semiclassical gravity?

what does string theory have to say about the trace anomaly in the expectation value of the stress energy tensor of massless quantum fields on a curved background and its interpretation as the ...
6
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377 views

Alcubierre warp bubble effect on gravity and space

I read the question Faster-than-light communication using Alcubierre warp drive metric around a single qubit?, and these questions came to mind: What kind of impact would an Alcubierre warp bubble ...
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62 views

How much additional light does Earth receive from the Sun due to Earth's gravitational field?

I was reading about how gravity affects light, and that got me wondering how much additional light is collected by the Sun due to the Earth's gravitational field. Is it a significant amount of light ...
4
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1answer
132 views

How warped spacetime bends trajectories of light and moving objects?

I fail to see why the light follows something like the blue line and not the green line on the attached image. Figure 1 - light bends around warped spacetime Afaik. something similar happens ...
4
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669 views

Gravitational attraction of triangles

Suppose I have two triangles relatively close together (so they probably shouldn't really be treated as point masses). I want to calculate the gravitational force (and potentially torque?) generated ...
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46 views

Can stable non-circular orbits exist in 2 or 3 dimensional hyperbolic space

I know that stable non-circular orbits in euclidean space exist only in 3 spatial dimensions but what about if the spatial dimensions are hyperbolic instead? Are there any stable non-circular orbits ...
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30 views

Mass Distribution Inside Sphere with Relativity

(Shell Theorem) If a mass is spherically symmetrically distributed within a spherical region, an observer measuring the gravitational pull from that spherical region would not know how the mass is ...
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1answer
90 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 ...
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48 views

Does gravity affect water permeability?

Suppose I have an approximately rectangular prism composed entirely of folded paper. If I place 600lbs on top of these rectangular sheets of paper, the paper should compress. How does this affect ...
2
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133 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 ...
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50 views

What $f(R)$ models pass most of the known constraints?

In most papers and talks about $f(R)$ gravity authors repeatedly state that the model proposed by Starobinsky 2007 $$ f(R)=R+\lambda\,R_{0} \bigg[\bigg(1+\frac{R^{2}}{R_{0}^{2}}\bigg)^{-n}-1\bigg] ...
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62 views

How much is time slowed down inside a planet or star?

An answer to What would be the rate of acceleration from gravity in a hollow sphere? states "that according to General Relativity time passes more slowly inside a hollow massive sphere than it does ...
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Two spherically symmetric shells of matter collapsing into a black hole

Suppose I have a thin spherically symmetric shell of matter of (rest) mass $M$ that collapses to form a black hole, and later a second thin spherical shell of mass (rest) $M'$, concentric to the ...
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1answer
94 views

Travelling through a worm hole

In every documentary I've seen about worm holes, I have noticed that they usually say that according to the General Theory of Relativity, there could exist worm holes called traversable wormholes; ...
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40 views

Does a lightning strike have a physical weight?

A lot seems to be unknown about lightning and it is possibly a source of dark energy at the instance of the strike. So if we were to place say a 10kg lightning rod (earthed) on a set of insulated ...
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37 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 ...
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17 views

Does a time-evolving gravitational field or potential have any important/interesting effects?

I have learned from classical electromagnetism that a time-evolving magnetic field gives rise to a contribution to an electric field, and vice-versa. Do gravitational fields have an analogous effect ...
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45 views

Has galaxy merger and universe expansion been proven?

I understand the basic argument for hierarchical merging of galaxies during expansion of the universe. I also understand peculiar motion and the Hubble flow. So I understand what's going on with ...
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99 views

What is the Casimir effect caused by gravity?

What is meant by a Casimir effect caused by gravity? Please explain me the concept in detail and how is it caused.
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15 views

Water tank, circulation, gravity

Is it possible to use gravity alone to make a water circulation system? -a large container filled with water and a hole in the bottom which attaches to a long hose/tube The other end of this ...
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33 views

Available material on Giant Gravitons

I am looking for a pedagogical introduction to giant gravitons (if one exists!). I have basic string theory/SUSY knowledge but no introduction to AdS/CFT. (Do I need to do some reading on AdS/CFT ...
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90 views

Propagator for massless spin 2 particle

In my quantum field theory class, we saw ad derived the propagator for both spin-0 and spin-1 particles, massless and massive. I am curious to know what the propagator looks like for a spin-2 ...
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39 views

Relative time difference and the gravitational potential of the geoid

I'm having trouble with something from a problem set on relativity and time. We are given the equation for time elapsed on a clock on the Earth's surface relative to time at the geocenter ...
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58 views

How would an observer feel the Einstein Thirring Lense Effect?

The Einstein Thirring Lense Effect, also known as Frame Dragging, is what happens when cellestial bodies have rotation. It states that when a body of mass is rotating around an axis it drags space and ...
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91 views

Visualizing bending of Spacetime around a heavy object

The commonly used example of viewing bent SpaceTime around a heavy object such as the Sun is the Trampoline. However, this image is limited as it shows only the bending below the Sun. What about the ...
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37 views

Muscular energy transformations with regards to gravity

Maybe this has more to do with biology than I know, but I have been wondering just what kind of energy muscles use and convert when lifting a weight off the ground or lowering a weight back to the ...
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45 views

What are laws regarding falling meteorites and the angles of descent?

I would like to know if there is any math / laws of physics governing the angle that a meteor falls on our planet. I doubt it falls towards the center of the planet, from what footage I've seen, it ...
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76 views

why ostriches cannot fly? physics explanation

I'm looking for a physics explanation concerning to the fact "The ostriches cannot fly". My statments: During the time interval $\Delta$t of the upward wingbeat, the ostrich drops a distance h ...
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78 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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51 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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57 views

How did the gravity of the particles/objects behave at the edge of the expanding universe moments after big bang?

During a very short time after the big bang, the universe must have had an edge of space-time which is very close to all the matter in the universe. The particles which are close to or on the edge ...
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40 views

Relative effects of forces

Excuse me for my ignorance but I really couldn't find a solution. According to Einstein, every happening is possible to describe by both of interacted objects. Is there any other way to describe the ...
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1k views

Visualizing Tension in FBD — Rope With Mass

Asked to find the tension of a point that is halfway up a rope (where the rope has mass), given the system: The solution of the problem (FBD included) is as follows. In this diagram (Tm = tension ...
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90 views

Einstein frame vs. Matter frame

What is the difference between Einstein frame and Matter frame in General Relativity? -A brief comment on each could be useful too. These two frames were used in this manuscript ...
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156 views

How do I measure the total weight of a container with scales on four corners?

I have a very large movable trash container, and I have mounted four scales, one on each corner. How do I get the total weight of the entire container? Is it simply a sum of the four weights, or is it ...
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147 views

Repulsive forces at large distances

I'm currently writing a 3D $n$-body simulator (similar to what you see here to simulate the evolution of a system of n particles under the force of gravity. It works fine for "smaller" scale ...
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461 views

Gravity change as a function of time only

Is it possible to find how gravity changes with time? That is, height is not part of the equation. For example, $g$ can be expressed as a function of height that does not involve time with this ...
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73 views

Could the attractive force of gravity be modeled as a repulsive force?

If space intrinsically contained gravitons of many different wavelengths then could gravity be model as a repulsive force simular to how casimir attraction works? or any other repulsive mechanism you ...
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44 views

A Global Measure on a Gravitational System

I am a computer science engineer and I am trying to simulate the gravity on my computer; several objects with different masses randomly distributed in a Three-dimensional space. I would like to ...
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64 views

Agreggating the masses and coordinates of a number of points to calculate their gravitational pull on an object in a single step

I have $n$ points, each of these have a set of coordinates and a mass; what I want to do is calculate the resultant force they induce on an object whose coordinates I also know. I can do that simply ...
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71 views

Gravitational Behavior of Rotating Body

Consider a stick with a (ball-shaped) weight at the end of it. Let's say this stick is in a state of rotation (it's floating in vacuum) and is also in a state of translational motion. Consider a ...
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89 views

How to get general relativity from linear gravity theory?

I know someone had done this study. Namely the field approach to general relativity. We can easily get an linear gravity theory. But it will be very complicated when we consider the ...
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96 views

accelerating a gravitational field

Newton's equation for gravity calculates gravitational force between two bodies $F= GMm/r^2$ My question is: How does the force change as these two bodies accelerate together through the universe and ...
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46 views

Gravity Interaction versus Gravity Well

This question may be misguided, but bear with me. Is there such a thing as gravitational 'invisibility', and if so, is it comparable to optical invisibility (photons/gravitons 'continue' in their ...
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79 views

Water Stream from a Horizontal Surface

If water was projected from a flat surface where gravity was equal all over the surface. What would happen when the water fell in on itself? The water is in a continuous stream and is perfectly ...
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554 views

What is the pressure in a vertical pipe that has moving fluid through it?

I have a system like this When the valve is closed, pressure along any point along the thin tube may be found thru pgh. 1. What about when the valve is opened? 2. Does the top of the jar need to be ...
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99 views

Where to go to minimize tidal forces?

Suppose you design an experiment where you need to minimize the effects of tidal forces. Where would you go? There are a few possibilities, and the choice depends on how much effort you are willing to ...
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96 views

If one were to move withing a tesseract, would the direction of gravity be different within each cell

If you unfold a tesseract into 3D space you get a cross shape (basically). Animated, it looks like the bottom most cube becomes inverted from it's 4D orientation. Would that mean that the pull of ...
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The cause of gravity

On the subject of the cause of gravity. Firstly, if you look at the terminal velocity equations Vt=sqr root(2 x m x g/density of the medium x A projected x Cd) if you use a globe with r=1 the Volume ...