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Questions tagged [gravity]

Questions regarding the attractive force which exists between any two bodies of matter.

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How does space time differ between galaxies? [duplicate]

Does the gravity wells differ enough between galaxies to have different speeds in space time? How much slower in space time would the biggest galaxy have compared to the Milky Way?
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Are there currently any planned or proposed missions to measure the gravitational fields of other planets in our solar system?

I just recently found out about the GRACE Nasa mission which basically mapped out the gravitational anomalies of earth as well as serving extensively in the study of earths geology and the movement of ...
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How does the size of a naked black hole effect its photon sphere?

What effect does the size of a black hole have on the size or density photon sphere and proximity to the horizon? If a person is in space looking at 2 black holes (one of them big and the other ...
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How would you relate the respective solar gravitational pulls of two planets?

I was asked this question: How much weaker is the gravitational pull of the Sun on Neptune at 30 AU, than it is on Earth at 1 AU? How would I even begin to determine this?
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Gravitational eddies across the galaxy?

I read about natural gravitational eddies that travel in a wave that black holes have. They also have a strong magnetic field. Does those eddies follow magnetic field lines of the rotating black hole? ...
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1answer
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What is the light that we see from a neutron star come from?

What hold the electrons in orbit? Is it gravity or the atomic attraction between the protons and neutrons? I asked this question on Physics SE I hope I improved on the quality enough to do better ...
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2answers
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Dark matter virtual objects hypothesis [closed]

I've hypothesized for many years in my head that dark matter are the gravitational after effects of objects that have exploded. My understanding of physics is that when an object explodes, its center ...
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240 views

Does Uranus have a stronger gravitational pull on its moons than Earth does?

I've read that Uranus has a lower surface gravity due to its lower density than Earth. However, does this mean Uranus has a weaker pull on its moons than Earth does for the same reason?
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Do unattached objects contribute to a planet's gravity?

If you could measure Earth's gravity with infinite precision, and did so both with Earth and its full population, and Earth with no people, would there be a direct difference in gravity? Is this even ...
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4answers
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Why does gravity make everything round?

I am studying ways to make an anti-gravity machine (!!). I believe it can be done, or theoretically be done using gravity itself as a "force" that pushes outwards instead of inwards. A similar ...
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Theoretical sudden appearance of a black hole in BBC drama show *spoiler warning*

I asked this on the ‘movies’ stackexchange site but they suggested I ask here, it’s a purely hypothetical query based on a BBC drama show called ‘Hard Sun’, feel free to kill the question if it’s ...
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Explain to a 4-year old why people below the equator are not tilted or suspended upside down

So I just bought a globe for my extremely inquisitive soon to be 4-year old son. He knows the very basics of the solar system and knows that we live on planet Earth and also knows the concept of ...
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1answer
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Behaviour of black holes

This question could be strictly linked to my another question related to black holes. It’s known that the horizon event is a place where dust,star components are ready to be incorporated to the ...
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1answer
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Is it correct to assume that the relationship between an objects mass and size, is what decides if it’s a black hole or not?

I’m asking this question in reference to a scenario I saw posted a couple of days ago, where it’s stated that if you would shrink earth to the size of a cherry, it would become a black hole. Is it ...
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2answers
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Gravitational attraction of Sun on distant object

A hypothetical situation which will help me with a real-life problem. Several stationary objects are placed at great distances from our Sun -- say 0.1 light year, 0.5 ly, 1.0 ly. Assuming no other ...
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If Earth had rings, how long would it take for the rings to loose orbit? [closed]

If Earth had rings, how long would it take for the rings to loose orbit? One of the answers in this question https://physics.stackexchange.com/questions/281828/if-earth-had-rings said we did at one ...
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What defines stationary vs spinning in space?

To produce artificial gravity on a space station, we simply spin it around some central point, and the acceleration makes objects "fall" outwards. If our space station is so far in deep space that it ...
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1answer
119 views

How much time does it take for a meteor (shooting star) to touch the ground after its combustion? [closed]

I know that meteors that We see as shooting stars travel tens of thousands of kilometers per hour and are tiny as a grain of sand, but after hitting the atmosphere and burn I suppose that its ashes ...
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2answers
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Why doesn't the Earth's rotation throw us off the surface?

The Earth is spinning at about a thousand miles per hour. Shouldn't we be thrown from its surface? Yes I know someone would comment "gravity" but physically we should be thrown from Earths surface. ...
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692 views

The size of the radius of the event horizon of a black hole created by the merger of a black hole binary system

Let's assume that you had a black hole binary system and everything said here is possible. Their large masses would lead to a large emission of gravitational waves. The loss of orbital energy and ...
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1answer
66 views

Maximum disturbance to space time of gravitational waves, and will this affect humans? [duplicate]

Do we have a theory that can tell us how much change gravitational waves can make to space time. If it is infinite then I think any time we can see biggest change in space time and how much could it ...
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2answers
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Assume that a star has a uniform mass density. Then how does the temperature scale as a function of the distance to the center?

Assume that a star has a uniform mass density. Then how does the temperature scale as a function of the distance to the center? Note: I am not looking for an answer that involves derivations or ...
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Explaining gravity assist to a 6-year old

We've been talking about Cassini with my 6-year old daughter recently and I've mentioned that it picked up more speed by passing close to Venus (twice), Earth and Jupiter. But then, I've struggled to ...
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2answers
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Does gravity repel when dark energy is involved?

So I am currently reading the book We have no idea by Jorge Cham and Daniel Whiteson. In one of their chapters they talk about how gravity is a force that only attracts and doesn't repel, most of the ...
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Is a perfectly circular orbit possible?

Let's assume that there is a perfectly spherical planet and there is a moon which is also perfectly spherical. Let's assume that there is no atmospheric drag and no other gravitational pull. If the ...
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How precise are the observational measurements for the speed of gravity?

General Relativity says that gravity moves at the speed of c. How precise are the measurements?
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Estimating the Rate at which Moon is Moving Away from the Earth

Here it has been discussed why the moon is moving away from earth at a rate of 1.5 inches per year. Is there any way we can estimate the value (e.g, 1.5 inches per year) mathematically?
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Is there something wrong about the gravity formula? [closed]

Help needed, please. I need the input of the experts here. I have always been troubled by the formula ..F = G * m1 * m2 / r^2.. , which appears to be counter-intuitive. It should be ...F = G ( m1 + m2 ...
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4answers
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Why is gravity only an attractive force?

As per the universal law of attraction, any two bodies (having some mass) experience a force of 'attraction' which is proportionate to ...and ...inverse proportionate .... Then comes my question: Why ...
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Earth shape and rotation

Imagine a helicopter that took off from point A and goes vertically in the air to a certain fixed point B in the atmospheric area at a certain fixed altitude with enough fuel to stay there (at point ...
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0answers
142 views

Shared moon in a double planet system

Would it be possible for two planets orbiting around each other to share a moon that orbits both separately? Would the moon in question would do something akin to a large figure 8 as it orbited both ...
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1answer
429 views

Can radiation affect gravity?

I was wondering if the sun's radiation affects the gravity when it passes through space? Like can radiation strengthen or weaken the force of gravity?
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What would happen if a person was out in space? would they get picked up by the pull of gravity from inbetween our planets, or sun?

I'm curious, if someone were to be floating out in space. Would they eventually be captured by the gravitational pull from another planet or sun. To be more specific the person isn't anywhere near ...
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1answer
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Pluto is fuzed to all the asteroids, comets, other minor planets, etc. Would it be big enough to hold an atmosphere without forming a tail? [closed]

Pluto is fuzed to all the asteroids, comets, other minor planets, etc. Would it be big enough to hold an atmosphere without forming a tail? All minor planets, asteroids, comets, etc that aren't ...
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1answer
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Wouldn't be “dark matter” better called “massless gravity”? [closed]

In spite of being a simple words game, that would make me feel less uncomfortable, as there could be a mysterious field still less mysterious than matter that passes through itself etc. Moreover, ...
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Does the inverse of gravity exists?

I am not talking about an antigravity effect that would cancel gravity, rather if there is a repulsive force, like when you use two magnets and flip one of them, where it becomes obvious that one is ...
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Can electromagnetic waves be affected by gravity?

Can electromagnetic waves change their properties in the presence of gravity?
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How strong would gravity need to be to prevent star formation

This question got me thinking. In another universe, with a different value for the gravitational constant G, how much bigger would G need to be for star formation to be prevented? In other words in ...
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Why does gas form a star instead of a black hole?

When a space gas gets pulled together a star is formed. On the other hand, when a massive star dies, it collapses to a black hole. You would think that the initial mass of the gas would be bigger ...
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Could Earth Sustain a Ring? [closed]

Unlike Saturn's moons our moon is relatively much larger in ratio to the size of the Earth. Earth's moon's orbit is also elliptical and is at a tilt to its equator because of this would a ring last ...
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1answer
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How would the barycenter of a double-planet system affect the two planets' surface gravity?

Assuming two similarly sized, tidally locked planets orbit a common barycenter, how would the gravity of the barycenter affect the surface gravity? For example, on the inner sides of the planets, what ...
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1answer
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How strong is the gravity from half of the distant universe?

I would like to know, how strong would the gravity be from the distant universe if we were somehow able to remove half of it. For example, if everything behind us did not exist, how strongly would ...
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1answer
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How strong is the gravitational stretch we experience from the edge of the universe?

How much gravitational effect do we experience (e.g. maybe -.00001 G or smaller) from the edge of the visible universe? By edge of the visible universe, I am talking about the region of the cosmic ...
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2answers
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Could Dark Energy be a “Cosmic Gravity Background”

Could dark energy (the accelerating expansion of the universe) be the result of gravity from the dense past universe "pulling" outward from all directions? The universe theoretically started out ...
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1answer
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Can gravity cause a Big Crunch, if the cosmological principle holds?

Say we have a closed universe that follows the cosmological principle. As a result, mass is distributed equally and, if as far as I know, gravity should have no net effect on the movements of galaxies ...
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1answer
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Effect of gravitation [closed]

When the sun reaches close to the centre of the Milky Way galaxy while revolving around it (like the earth closes down on the sun while revolving around it, perihelion), will the gravitational effect ...
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1answer
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What is “superficial gravity”

I have seen the term superficial gravity used and it seems to be equivalent to surface gravity seen, e.g., here http://arxiv.org/pdf/1701.02295 Is there any difference between superficial and ...
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Is there a better explanation of Hawking radiation?

I'm writing a piece on Hawking radiation, and find I have something of a problem. The "given" explanation which I find on Wikipedia and elsewhere is unsatisfactory: "Physical insight into the ...
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1answer
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How large can a ball of water be without fusion starting?

How large can a ball of water be without fusion starting? Peculiar question: some explanation might be necessary. My young son is into ‘space’ and astronomy. One of his posters says that Saturn could ...
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1answer
272 views

How can artificial gravity hold the water in swimming pool? [closed]

I was watching Passengers (2016). In this movie, a swimming pool exists in the space station. In middle of the movie, Artificial Gravity is turned off and the water rises, with the swimmer suffocating ...