# Questions tagged [gravity]

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

370 questions
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### Will a Ball placed close to Sun fall into it?

Like a ball falls on the earth due to gravity, if suppose we are able to place a ball close enough to the sun. Will the ball fall into the sun due to its gravity or will it be pushed away due to its ...
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### Do planets migrate suddenly or gradually?

Current models of the configurations of the planets conclude that Neptune once migrated outwards. AFAIK this refurbishment came about by Jupiter and Saturn gradually getting into and leaving a ...
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### How was the hypothetical ninth planet kicked so far out of the Solar System?

I was reading this article on science news and ran into the following statement: Such a remote super-Earth probably originated closer to the sun only to be kicked out by the other giant planets ...
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### Gravity assist: why is the velocity doubled? [closed]

The Wikipedia article has this terrestrial analogy: Imagine standing on a train platform, and throwing a [tennis] ball at 30 km/h toward a train approaching at 50 km/h. The driver of the train sees ...
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### Formulae for gravitatitional equilibrium

I am trying to calculate at which point gravitational equilibrium sets in for various bodies (planets stars neutron stars etc.) assuming they are perfect spheres. However, the radius I get is not ...
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### A phonecall inside a blackhole

I was wondering what a phone call would be like entering or falling t=into a black hole. Due to the massive density of the black hole and time would feel slower, how would that appear to the person on ...
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### What is the Maximum Speed that can be acheived Because of Acceleration Due to Gravity?

Planets and other bodies in the universe have different ranges of gravitational fields. What is the maximum speed that can be achieved because of acceleration due to gravitational field. In other ...
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### Black holes and time relation

Why Is it said that if someone is being sucked inside a black hole then he/she may see that time is running slowly?
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### What if we throw two solid objects parallel in space? Do those two objects have any chance to collide with each other?

What will happen if just throw two solid objects (for example, solid footballs) parallel in outer space and those two objects are floating and going far away in the universe. So is there any ...
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### Where does Jupiter's gravitational force come from? Why don't Jupiters gasses fly away?

Gravitational force is the attractive force between any two masses. What about gaseous planets, where do they get their attractive force from? While the big rocky planets don't have enough ...
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### Camera reaching the event horizon

This question came to my mind after reading this. I think it is safe to assume that the supposedly thrown camera would not reach the event horizon in one piece. So my question is : If I dropped a ...
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### What is the gravitational force felt on Earth from the other planets in our solar system?

How much gravitational force is felt on earth from the other planets in the solar system? The sun exerts the strongest g-force, holding us in it's orbit, followed by the moon which affects the tides ...
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### A camera and time dilation?

If I travelled near a black hole, my time would progress slower relative to someone on Earth. This is clear enough. However, what if we sent a probe with a camera to a black hole? When we watch the ...
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### Is the sphere of influence of our milky way's center super massive black hole same as the Milky way's radius?

The sphere of influence is a region around a supermassive black hole in which the gravitational potential of the black hole dominates the gravitational potential of the host galaxy(found it in wiki). ...
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### Do asteroids have a gravitational field?

I know that asteroids are huge chunks of rock, orbiting a solar system. Do asteroids have a gravitational field and do they gravitationally attract each other to form planets?
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### Why can't gravity repel things?

Gravity is the result of the curvature of space, so could the curvature actually send objects away from the source?
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I wrote an experiment in HTML5 and Javascript to try to show what is happening to the curvature of spacetime as a body moves through a region. As time progresses, I'm using the ...
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### Does gravity bend light, and how much time does it take for light to cross gravity of a Black Hole?

This is very confusing to me, so the question might be same. Please go through it, if required i will add more text. According to Einstein's theory of general relativity, photons are not technically ...
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### Understanding gravity

Forgive me if my question has an obvious answer, but I need to know the answer. I always thought that more massive/energetic objects had a stronger force of gravity than less massive ones; that is, ...
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### Can we simulate Earth's gravity in space?

Earth gravity is 9.8 $ms^{-2}$ Gravity on ISS(international space station) is 8.2 $ms^{-2}$ approx. As per this https://physics.stackexchange.com/questions/29929/gravity-on-the-international-space-...
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### If any object could become a black hole, could any object become a neutron star?

A black hole doesn't necessarily need to form from a star; theoretically, it could form from any extremely dense object. In fact, many astronomers differentiate certain black holes, like supermassive ...
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### Does Dark Matter affect the motion of the Solar System?

Would dark matter have a similar effect on the Solar System as it does on the Milky Way? I'd imagine it could help hold together some of the Solar System bodies or at least affect their motion, right? ...
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### What's the difference between the apparent horizon and event horizon of a black hole?

The Wikipedia page for apparent horizon is pretty sketchy and requires some GR knowledge. Is there any simple definition?
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### If the Universe is infinite, would heat death be impossible?

If the Universe is infinite, one would imagine that if we kept moving through space, we'd constantly find newer and newer galaxies and objects forever. This would imply that there is an infinite ...
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### Gravitational red hift vs Doppler redshift: Is the universe really expanding?

Is it possible that the redshift observed by Edwin Hubble is really from a gravitational redshift and the universe isn't expanding as he has predicted? What I think I know thus far is this: Redshift ...
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### Why does gravity increase in star formation?

When a star ignites ( ie. fusion starts ), the star maintains its form by balancing gravity's inward pressure, and radiation's outward pressure. I get that the fusion of hydrogen atoms releases ...
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### Is a black hole a perfect sphere?

I know all about how black holes form and why their gravity is so strong. However, is the gravity equally powerful in all directions? Will the event horizon appear as a perfect sphere?
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### Gravitation - Pulling or Pushing force?

According to Newton, gravity is the pulling - or in fact the attracting - force of any heavenly body towards any object to its center. But, to the contrary, Einstein once said that the four dimensions ...
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### How gravity works in a black hole? [closed]

In astronomy class, we have to state how gravity work in the black hole? I know for one fact is that black hole is strong enough to stretch you thin enough like a noodle. Any ideas?
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### Strength of gravity during the big bang?

I was watching a documentary on the big bang, one of the astronomers said that initially the four fundamental forces were combined as one, they then emerged to become: The strong and weak nuclear ...
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### Does more ocean on an Earth analog produce a different rotation period?

Would an exoplanet that has more ocean than Earth rotate at a different speed as a result of this? Would the amount of water impact the weight, gravitational pull, and/or tidal forces and cause a ...
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### What causes objects to become tidally locked?

I'm trying to write a gravity simulation (suns planets etc), and was hoping tidal locking could be one feature demonstrated. Using a simple equation for gravity has produced some interesting results, ...
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### Could there be dark matter black holes?

Could dark matter compress and form black holes? Since dark matter is even more abundant than normal matter, a dark matter black hole should not be rare...right?
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### How does light so travel so fast?. [duplicate]

I've read that photon's have zero mass, hence no force is needed to accelerate them. But then the second question. How can gravity affect something which has 0 mass?. Yes, gravity(black hole) can bend ...
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### If 50 tons or more of debris falls to earth everyday, is Earth getting heavier?

In turn, would that increase our gravitational pull?
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### Why do objects all orbit in the same direction?

In a solar system or a planet that has many moons, why do their orbiting objects all orbit in the same direction? Is it possible for two orbiting masses to orbit in the opposite direction of each ...
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### Is expanding universe adding potential energy?

A system with two massive bodies has potential energy proportional to their separation. Since the universe is expanding, is the potential (and total?) energy of such a system slowly increasing? What ...
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### What would Earthlike planets bigger than Earth with <10 m/s^2 gravity and complex life be like? [closed]

Large is bigger than Earth. Assuming that such planets exist (though I guess if such planets don't exist that would explain much of the Fermi paradox). Maybe some amount of iron is needed though, to ...
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### Can stellar black holes cancel each other?

Hypothetical question: when a pair of identical stellar black holes are very close to one another wouldn't the side facing each other experience lower gravitational force? How is this logic un/sound?
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### How long until the Earth and Moon become a binary planet?

With the rate at which the moon is further receding into a higher orbit, how long until the barycentre between us and the moon leaves the earth, and going by the IAUs 2006 definition update, we become ...
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### Semimajor axis variations in co-orbital moons

I've been playing with simulations of co-orbital bodies similar to Saturn's moons Janus & Epimetheus- horseshoe orbits where the two bodies are of comparable mass- and I'm seeing some very odd ...
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### How small would you have to crush an object for it to become a black hole?

I was wondering how much you had to crush an object for it to become a black hole. Recently I learned that anything could become a black hole (even you) if it were crushed down small enough, for ...
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### Stability of solar system

My question is simple: Is the Solar system stable? You can see this Wikipedia page. Edit: Sorry, because i think my question is more about mathematics and classical mechanics of planets in ...
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### How can Halley's Comet be predictable?

How can we know that Halley's Comet is going to come again every 76 years? I understand that the comet has an orbit around the sun but how can scientists know that it won't be thrown off course for ...
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### How does gravity interact with a photon?

If photon is mass-less and gravity can interact only with matter, then how does gravity alter the trajectory of light?
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### Why doesn't the sun pull the moon away from earth?

If the suns gravitational pull is strong enough to hold much larger masses in place (all the planets) and at much greater distances (all planets further away from the sun then earth) why does it not ...
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### “Up” and “down” in Space [closed]

From my understanding, "up" and "down" in space is going towards (down) an object's gravitational pull or (up) which is going away from it. I get confused with this explanation, and I believe simply ...
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### On a log-log plot of surface gravity to planet mass, what is the meaning of the y-intercept?

I am playing around with data from exoplanets.org, and am interested in the plot of surface gravity to planet mass. I reproduced this plot after downloading their data and performed a non-linear ...