# Tagged Questions

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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### How do you travel in a circular orbit around a massive body?

I am trying to figure out how an object could achieve a perfectly circular orbit. Given a mass for the planet or other body the object is orbiting and a distance from the center of mass, how fast ...
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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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### Is the gravity between objects other than celestials observable? [duplicate]

I've always read that all matter has gravity. But, can we observe it? I mean, The Earth pulls us but what about small daily objects? For example, if we release 2 small objects in space, do they get ...
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### Is it possible to create artificial gravity by magnetizing iron in the blood stream?

I have been thinking is it possible that using a rather strong magnet on the human body's blood stream we could enact a small case of artificial gravity on the human body via the iron in the ...
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### General relativity theory [duplicate]

As I understand general relativity theory (please correct me if I'm wrong), time becomes dilated and space becomes compressed around mass, and this is responsible for gravity. I'm struggling with ...
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### What happens after a rocket is fired with velocity equal to or greater than escape velocity? [closed]

When a rocket is fired a speed greater than or equal to escape velocity, then it does not have any gravity effect of the earth. So, suppose if a rocket is having that much energy which will only last ...
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### Gravity as a gauge theory

Currently, (classical) gravity (General Relativity) is NOT a gauge theory (at least in the sense of a Yang-Mills theory). Why should "classical" gravity be some (non-trivial or "special" or extended)...
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### What keeps a gas giant from falling in on itself?

There is not enough gravity at the center to start nuclear fusion, but it seems that there would be plenty enough to collapse the planet.
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### Has anyone measure the strength of the force of gravity in relation to the molecular bonding? [closed]

It's clear to me that gravity it a function of mass. It is also clear to me that gasses are less affected by gravity. So I'm thinking that there exists a measurable minimum binding distance $d$ ...
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### Basic Question About General Relativity?

I'm a layman that loves Physics. I'm also horrible at math. Having said that I have many, many questions in regards to physics and General Relativity in-particular. I will try to keep my question(s) ...
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### Is the Higgs field really disconnected from gravity?

I would like to understand better the role of Higgs mass in the gravitational interaction. I read here in some posts, that the Higgs mass has nothing to do with gravitation. Is it justified to say ...
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### Barbells and gravity

A giant set of bar bells floating in space (like two identical sized planets connected by a long rod) would have a centre of mass midway between the two on the connecting rod. But surely it would ...
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### 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 ...
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### Closed form for shape/tension of an elastic cable slung between two points

Given the 2D coordinates of two points, $a$ and $b$, between which an elastic cable of known length, $l$, mass per unit length, $m$, and the spring constant, $e$, is slung, I need to compute the shape ...
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### what is the speed of gravitational interactions? [duplicate]

Example. Two bodies with masses m1 and m2 distance between them one year of light. What happens to the force of attraction between the two bodies when one body suddenly disappears? Is the force ...
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### A Hollow Black Hole

I was just reading a question about the gravity inside a hollow neutron star. It was a trivial question, obviously there is no force felt. But then it got me thinking. Suppose you had a hollow sphere ...
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### Gravity in the center of a hollow neutron star [duplicate]

Imagine a hollow 100 metre diameter (for example) sphere made of incredible dense material (ie neutron star dust etc) but is self supporting (ie the central cavity). Assuming that the sphere skin is ...
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### Can the mass of an orbiting object and the object being orbited be determined by the distance and orbit velocity alone? [duplicate]

This question is the inverse of: "Could an object orbit while moving at twice the speed, but at the same distance, if it had half the mass?" I'm curious about the nature of orbits, but am not well ...
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### Understanding black holes [closed]

Basically I don't know anything about Physics but I am really curious about all these things. I was trying to understand what is a black hole, but unfortunately I couldn't figure out from online ...
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### How could vacuum energy cause the expansion of the universe? [duplicate]

Is it by gravity? How could gravity produce a repulsive force?
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### In which direction do gravitons travel? Do they originate from mass or are they collected by masses?

This is a kind of silly question, that mostly goes unanswered: are gravitons detatched from the objects they act on, like photons in free space. Maybe gravity or gravitons are collected by mass (...
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### Is there a way to fill Tank 2 from Tank 1 through Gravity alone?

I am a newbie in water system design but I am currently faced with the exact situation below on my land, and I need to know whether gravity alone is sufficient in order to fill Tank 2 from Tank 1, as ...
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### Is Newton's universal gravitational constant the inverse of permittivity of mass in vacuum?

Is it possible to consider Newton's universal gravitational constant, $G$, as inverse of vacuum permittivity of mass? $$\epsilon_m=\frac {1}{4\pi G}$$ if so, then vacuum permeability of mass will be:...
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### Negative Energy and Wormholes

Apparently to create wormholes you need negative energy/matter. Say you had negative matter/energy, how would it be applied towards making a wormhole?
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### Gravitational Field from Irregular Object

How does one calculate the gravitational field of an irregularly shaped object? I was thinking specifically of the gravitational field due to a human, and tried to see if modeling a human as an ...
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### Map of the gravitational strength of the solar system

I am looking for a map or plot of the gravitational strength in the solar system. In an ideal world there should be something like google earth to move around in the solar system, zoom in and out and ...
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I've asked wether artificial gravity, as seen in some SF-Movies, would violate known laws of physics. To recap, my idea of an Artificial Gravity (AG) system was like this: A Device that creates an '...
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### 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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### Expressing a force in components [closed]

If there is an object on some ramp, how do I express its weight in terms of vectors orthogonal and parallel to the ramp surface? For example, if the object has a weight $\vec W=m\vec g$, then how do ...
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### Physics and math behind flight through solar system: Where to start?

I wrote a first program that simulates a solar system. I was able to calculate the locations for every planet on its elliptical route for any given time. In a second program i managed to simulate ...
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### Mass - Gravitational pull - centrifugal force

In relation to mass/gravitational/centrifugal force. Is the increased gravitational force due to the increase in mass of a planet (i.e. earth) from meteorites, etc.. directly proportional to the ...
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### Einstein action as a functional of the tetrad (first order formulation of gravity)

Let the Einstein-Hilbert action be rewritten as a functional of the tetrad $e$ (units shall be set to $1$) such that $S_{EH}(e)=\int \frac{1}{2}\epsilon_{IJKL}~e^I\wedge e^J\wedge F^{KL}(\omega(e))$, ...
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### What forces are at work causing sand to migrate to the centre of a spinning bucket of water? [duplicate]

A bucket is filled with water and a handful of sand. The water is then spun. Why and what forces are in play which cause the sand particles to congregate in the centre of the bucket?
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### Graviton through the horizon and force felt outside a black hole [duplicate]

Gravitational force is mediated by graviton exchange. If I am standing outside a black hole, I can of course feel the attracting force towards the black hole. This should correspond to gravitons ...
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### the higher you go the slower is ageing [duplicate]

as per to einstein as we go far from the earth the TIME tends to slow down , so it means when I am one metre above the earth's surface , the time has slow down for me as per http://en.wikipedia.org/...
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### Gravity is an intrinsic property of every atoms? [closed]

If gravity is the force of attraction between masses, does this force is an intrinsic property of every atoms? Is there any possibility of some other particles within atom which is yet to be ...
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### Is there a relation between the magnetic field force of the earth and the gravitational force between the earth and other bodies? [closed]

According to Newton's Universal Law of gravitation, we can say that a huge body of mass will attract another body of mass within a short range, however, if both bodies are for instance magnetic, ...
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### Can we disprove Artificial Gravity (like in the movies) with a thought experiment?

Suppose you have a Device that creates an 'artificial gravity' (AG) inside a Box, with these properties: the system does not use inertial forces (like centrifugal force) or a huge mass to create AG ...
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### What causes matter to initially rotate/spin/orbit?

What causes matter to initially rotate/spin/orbit? All I can find is the statement that in space particles of dust/gas/matter contract into a spinning disk due to gravity (to form stars, solar systems,...
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### What happens with the force of gravity when the distance between two objects is 0?

so I had my first approximation to the gravity equation $$F=GmM/r^2$$ and some questions arose that my teacher couldnt respond: if r approximates to 0 with mM being ...
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### Can one black hole suck in another black hole?

In the recent news, scientists at NASA have found “unprecedented” black hole cluster near Andromeda’s central bulge. I wonder why doesn't all these black holes merge and such each other in until just ...
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### is gravitational force dependent on objects radius?

I was told that objects with the same mass but different sizes (or densities) will have a different gravitational pull. Is this true? If so, why?
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### How did the scientific community receive this measurement of speed of gravity

This link and this one concern a recent measurement, by Chinese scientists, of the speed of gravity using Earth tides. They find it is consistent with a speed equal with the speed of light, with an ...
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### How general relativity gets to an inverse-square law

I understand that a general interpretation of the $1/r^2$ interactions is that virtual particles are exchanged, and to conserve their flux through spheres of different radii, one must assume the ...
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### Properties of gravity

If all objects in the solar system suddenly went cold to the core, including the Sun, would it gravity play any different role? I guess what i am trying to ask, is there any relation between energy ...
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### How does energy convert to matter? [duplicate]

To my understanding, matter and energy are one and the same. Shifting from $E$ to $M$ in Einstein's famous equation requires only a large negative acceleration. If $M$ really is $E/c^2$, does that ...
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### Expected behavior of the gravity under some experiment [duplicate]

I would like to know the expected behavior of the Gravity under the following mentioned imaginary experiment: What if we dig a well or a boar or a straight hole (say, its diameter is 100 meter) ...
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### Physics of donut magnets levitating vertically on a pencil?

When you put identical donut magnets on a pencil horizontally, the magnets all repel from each other in a way that creates equal spacing between each magnet. However, spacing is not equal when the ...
A simple pendulum, $20cm$ in length, has the period of $2.7s$ on a certain planet. Find the mass of the planet if its diameter is $18000km$. $G=6.67\times10^{-11}Nm^2/kg^2$ I have no idea how to get ...
I'm trying to analyze the motion of the particles which exert the gravitational force each other. Let $M_1$, $M_2$ be the masses of the particles, and the equation of motion of particle $M_1$  F=G\...