Questions tagged [gravity]

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

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1answer
592 views

The role of gravity during planetesimal accretion

As far as I understand, during the formation of a planetary disc, grains of dust stick together due to collisions and chemical bonding. Considering the size of the grain - say, 1 mm - and the speed - ...
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2answers
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What is the orbit of Earth around the Sun?

According to wikipedia and other sources, a planet and a star always move in a circular orbit around the common center of mass of the both bodies, in case of Earth and sun, this center of mass lies ...
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Do planets repel?

I know gravity is the result of mass. Gravity is nothing but the attractive force on a body due to its mass. I have a question that may be silly. In magnetism we have attraction and repulsion. Earth ...
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Is Jupiter made entirely out of gas?

I heard that Jupiter is made out of gas. But in school I learned that Jupiter has gravity which is 2.5 times that of Earth (Gravity that can tear apart a comet) and gravity is proportional to mass. ...
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6answers
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Why are stars so far apart?

So, this is mere musing, but it seems that stars are quite extremely far apart. I tried to determine the mean distance between nearest neighbors for stars (in just our galaxy) but I'm not sure what it ...
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What is the most oblate astronomical object known?

There are some very vast spinning objects out there. How high can the eccentricity get, or, which I think is easier to understand, how small can the ratio between the polar and equatorial diameter ...
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537 views

What are the arguments against the Feng and Gallo thin disk explanation of galactic rotation curves?

The well-known galaxy rotation problem is described here. Basically (as one moves outward from the galactic centre, $R$ increasing) the observed pattern of variation in orbital speed $V$ is very ...
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How to convert a gravitational force to speed and direction

I am doing some calculations, and I wanted to know that after using the gravity equation, $$F = G \frac{m_1m_2}{r^2}$$ if you can use $F$ and convert it into a speed, such as km/year, and also a ...
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Are our 'observations' of or near a black hole affected by gravity induced time dilation?

This answer made me wonder if matter/energy/events near a black hole are viewed (by us) in a very different time frame, how might that affect our measurements? ...
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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 ...
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Why does the distance between Sun and Earth stay the same?

Well, we all know Sun gravity , makes the Space time curvature and space pushes the earth towards the Sun. But my question is "why the distance between the Sun and Earth is Same? Earth should have ...
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2answers
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Can the theory of multiverse explain dark matter?

If there are many universes, they must have a gravity effect on each other. Since dark matter is measured through gravity, but we don't know the mass behind it, isn't it possible that it comes from ...
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Why does a particle feel no force at radii greater than itself?

I am working through Liddle's "An Introduction to Modern Cosmology", and in a newtonian derivation of the Friedman equation he states: in a spherically symmetric distribution of matter, a particle ...
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Will Earth lose the Moon before the Sun goes into supernova?

Ive read on some sites and saw on youtube videos that the moon is getting away from earth by 1-3 cm a year. Is this enough to make the Earth lose the Moon before the Sun goes into Supernova? Im ...
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461 views

From what distance can one object influence gravity of another object?

Each object in the universe has its own gravitational influence on all other objects in the universe. What distance do they have to be from each other to create only one gravitational influence? ...
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2answers
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Is gravity a source of infinite energy at a cosmological scale

As I understand it, gravity cannot be attenuated by any medium (in the way that EM radiation can be, for instance). Does this, then, not make it a source (theoretically, I am not talking of ...
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Why don't small stars end up as a black holes?

I have recently done some research into black holes, and realized that big stars form black holes, whilst smaller ones don't. Is this because the gravity isn't strong enough for it to fall in on ...
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Exercise: 2D orbital mechanics simulation (python)

Just a little disclaimer beforehand: I have never studied astronomy or any exact sciences for that matter (not even IT), so I am trying to fill this gap by self-education. Astronomy is one of the ...
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1answer
242 views

Black Holes, how do they form?

Do black holes form by when the massive star dies and all the gravity falls in on itself, or something else. Please let me know, I'm really desperate!!
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1answer
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Is it accurate to say that we have a gravitational attraction towards all objects in the known universe?

Its probably small, but is there a theoretical gravitational attraction between all objects in the universe? Light can move pretty far, so does that mean gravity can as well, and is the gravity ...
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How much would you weigh if Earth stopped orbiting the Sun? [closed]

I have a curious question. The reason why astronauts are weightless in space is because they are orbiting Earth. If they suddenly stopped orbiting they would fall directly into Earth. Earth is doing ...
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4answers
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What happens if gravity shuts down for only one second? [closed]

What would happen if gravity completely stopped for 1 second?
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How can astronomers determine the difference between “hydrostatic equilibrium” and “just happens to be spherical”?

This is relevant for the definition of a dwarf planet. I presume the answer will be, well, if we can tell the mass of the body and guess the material. I don't find this very satisfactory because (1)...
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Apocalypse on earth

What would it feel like on Earth if the Earth accelerated due to sudden changes in the solar system like ejection of another planet? Would there be giant tidal waves and other cataclysmic events?
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Brain vs galaxy [closed]

The number of neurons in the human brain is equated with the number of stars in the Milky Way. Could the Milky Way act as a consciousness of its own, with the gravitational strength between the stars ...
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3answers
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Is there any way a meteor can hit at less than escape velocity?

Note: I have figured out one case: The meteor is splash from an impact on a close-in moon. I'm looking for any path from deep space. My understanding is that anything from deep space will ...
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Why isn't the star that created the black hole a black hole?

If the mass of a black hole is creating so much gravity that light cannot escape, why isn't the mass of the star that created the black hole (before it went supernova) trapping light as well? By all ...
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What is the difference between Sphere of Influence and Hill sphere?

Wikipedia's definition of Hill sphere is: An astronomical body's Hill sphere is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit ...
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Can you explain the pattern of Hill sphere sizes of the objects of the Solar system?

I found this image on calculations of Hill sphere for planets/dwarf planets of the Solar system. From http://en.wikipedia.org/wiki/File:Hill_sphere_of_the_planets.png I found it interesting that ...
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Are there sufficient observational data to measure non-Newtonian perihelion advances of any Asteroid and Comet orbits?

Anomalous (i.e. not predicted from Newtonian theory) advances of the perihelion direction have been observed for many solar system planet orbits and have been accounted for by Einstein's General ...
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any unique phenomenon when the cores of two planets are aligned with their star's core?

Imagine a line passing through the cores of two planets (in the same planetary system) and their star. Have we ever witnessed this - either with both planets on the same side of the star or on ...
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Electron Degeneracy Pressure and the Pauli Exclusion Principle

I have read that what keeps white dwarfs from gravitational collapse is electron degeneracy pressure. How does this pressure prevent further collapse, and how is it related to the Pauli Exclusion ...
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1answer
149 views

Under Earth's gravitational pull, how dense would an object have to be to reach its Schwarzschild Radius?

The Schwarzschild Radius is a theoretical radius, that if the mass of the object was compressed into that certain radius, the escape speed from the surface of the compressed object would equal the ...
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How massive does a planet need to be to create gravitational lensing?

Is it ever possible for starlight to be distorted in a noticeable way from something as small as a planet? I'm guessing that the chances of this working are better on a dense terrestrial planet than ...
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How does a gravity slingshot actually work?

From what I know of elliptical orbits, an object speeds up near the periapsis and slows down at the apoapsis, much like we learned in high school physics how a sphere would roll down and back up a ...
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What is the time/size/rigidity ratio for a space object to become mostly round?

In the answer here multiple comets are identified that do not form a single round body. A drop of water will form a round shape in the time it takes to free fall a couple of feet. All of the ...
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Is the influence of gravity instantaneous?

When I was in college, I posed to my astronomy professor a thought experiment that had been puzzling my mind for some time: "If all the matter in the Sun magically disappeared instantly, how long ...
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1answer
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Is there a radius inside of which objects are (doppler) blue shifted?

The Andromeda galaxy is about 600,000 light years away and is doppler blue-shifted. Are there objects closer to us than Andromeda which are red-shifted? Are there objects farther than Andromeda that ...
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1answer
473 views

Finding the radius of an eccentric orbit at any point

Knowing the apoapsis, periapsis and therefore period of an orbit, how can I find the radius of an object in an orbit at a given angle or time, whichever is needed. For example, if I have an object m ...
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Could light be dark matter?

Is it possible that light itself is dark matter? I am speaking of photons (e.g. visible light, infrared, ultraviolet, etc...). I realize light is understood to be massless, but it is obvious it at ...
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1answer
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What is the physics of a gas mass subject to gravity in space?

There are many formulas for atmospheric pressure on earth, but how does gas behave in free space? I am thinking about why stars form. I am guessing that the gas density will influence pressure, as ...
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2answers
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What is gravity really?

What is gravity? I want to know more than it being simply the "mysterious force" that attracts things to earth. Is it a particle, a wave, or something else entirely?
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1answer
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Dark Energy Expansion

The new Cosmos extra features mentions that at about 6,771,500,000 years ago the universe began an accelerated expansion. How do we know this? What evidence do we have for this renewed and accelerated ...
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1answer
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Could dark energy be negative gravity?

Main question: Could dark energy (the mysterious accelerating expansion of the universe) be explained by "negative gravity"? "Spin off" questions: Does antimatter have negative gravity? If ...
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1answer
643 views

Is it safer to be near a star or a black hole?

If a star or black hole neared the solar system, which would do the least damage? For the sake of a good comparison, lets assume the candidate star is an "average" 5 solar mass star, and the black ...
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Using the Sun as a Gravitational Lens

Can the Sun be used as a gravitational lens to achieve better telescopic viewing? Can this effect be practically used to view celestial objects?
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1answer
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If Mars orbited the Earth how distant would it have to be to cause the same tides?

If it were possible to replace the Moon with Mars, how distant would it have to be to essentially create the same oceanic tides as the Moon currently does? Mars seems to be roughly 3 times the mass of ...
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1answer
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What is the optimal escape trajectory from near a black hole?

Consider a space ship that is being drawn closer to a black hole. The crew begins to notice the effects, and discovers that they are nearing the black hole. They then manage to halt their ...
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Dark Flow: statistical limits on existence

Dark Flow has been thrown around as a term a lot lately, especially with the latest Planck results. New Scientist reported last year that it was now statistically improbable, but the paper by Atrio ...
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Would time go by infinitely fast when crossing the event horizon of a black hole?

If you were to fall into a black hole, my understanding is that from your reference point, time would speed up (looking out to the rest of the universe), approaching infinity when approaching the ...