Questions tagged [gravity]

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

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6
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3answers
5k views

Is Earth's Surface “In orbit”?

I'm having trouble understanding relative angular/tangential speeds at increasing altitudes above Earth's surface. In particular, I find this comparison of tangential velocities on Wikipedia very ...
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How to determine the orbital period of an asteroid using Kepler laws given its orbit's radius?

Given that the mean distance of an asteroid from the Sun is $450 \times 10^6$ km is it possible that the asteroid completes one rotation around the Sun in two years? According to the third law of ...
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Gravity as a Fluid and Repulsive Force [closed]

I have looked this up in depth including the work by Le sage and Fatio where they posited gravity as a repulsive force and based their calculations on gravity as particles in motion acting on ...
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1answer
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Can we use Breakthrough Starshot spacecraft to detect any unknown massive object in our solar system?

For example, the hypothetical Planet Nine. Since we just want to prove or rule out the existence of Planet Nine in our solar system, we can avoid most of the technical challenges for StarChip (camera ...
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Gravitational Properties of Asteroids

How large would an asteroid have to be in order to hold a person so that the person could not escape?
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Rocket Equation from Newton’s 3rd Law, Force of Gravitation, and dp/dt

I am using the derivative of momentum (dp/dt) with Newton’s 3rd Law with the gravitational force of Earth.   $$ F - F_{gravity} = \dfrac{\mathrm{d}p}{\mathrm{d}t} \\ F - \dfrac{G \, m_e \, m_r}{...
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1answer
72 views

How is Earth's gravity modelled?

The Earth does not have a defined geometric shape. Then how do space scientists who want to put a satellite in orbit model the gravitational field of Earth? Do they assume a single object with minute ...
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78 views

Does the Lagrange L1 point have a 'size'?

Like in cubic kilometers, what is the size of L1 "area of influence"? being unstable I guess that size can vary?
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1answer
128 views

How much volume of gases could be added to Mars atmosphere that the planet gravity can retain?

This article Mars atmosphere states that Today Mars atmosphere is very thin, but it was not always like this. Around 3.5 billion years ago, the red planet had a thick enough atmosphere for liquid ...
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1answer
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Where would an object fly to if it were to leave the gravitational field of Earth? And would it stop somewhere? What would happen to it?

My 3,5 year old son is asking :-) He can take answers for a 15 yo I think. Many thanks for your help!
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2answers
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The dominance of Gravity vs Strength and its dependency on crater size

So I am trying to write a research paper (about 3700 words) for high school about the topic "The dominance of Gravity vs Strength and its dependency on crater size" or something similar. I have ...
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2answers
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How does the Moon's gravity affect Earth's oceans despite Earth's stronger gravitational pull?

Given that Earth has a much stronger gravitational pull than the Moon, how does the Moon have any influence on Earth's oceans?
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1answer
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Have more recent LIGO/VIRGO gravitational wave measurements narrowed down the speed of gravity further?

This answer to How precise are the observational measurements for the speed of gravity? says: ...in 2013 a Chinese group built a model using Earth's tides that helped them narrow it down. ...
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1answer
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Do gravitationally bound (e.g. orbiting) objects really resist the expansion of space?

Thinking about the expansion of space, it is commonly explained that gravitationally bound objects (like galaxies and galaxy clusters) will not be affected by the expansion of space (dark energy). I ...
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2answers
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Black hole's gravity

Is gravity relative to volume, or size of an object? Since a black hole is a massive star that collapses on its weight, how comes the same sun's mass, when it becomes a black hole, provides gravity ...
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1answer
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Could the rotation of a black hole cause other planets to rotate?

Because everything rotates so perfectly, and we know that some blackholes rotate and they're the biggest things in the universe, so a silly question comes to mind. If you remove all black holes from ...
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Why aren't globular clusters disk-shaped? [duplicate]

I thought that solar systems and galaxies are disk-shaped because that is the most stable shape under gravitation. Globular clusters are very old, often times older than their host galaxies, so why ...
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1answer
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Why can't supermassive black holes merge? (or can they?)

The CNet article Astronomers discover two supermassive black holes in a death spiral links to Discovery of a Close-separation Binary Quasar at the Heart of a z ~ 0.2 Merging Galaxy and Its ...
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3answers
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What effect does Earth losing a part of its mass have, is there an impact on the Earth's orbit around the Sun?

This is a random question that popped into my mind. I'm not a physicist or astronomist, however, I am genuinely curious. Also, this is not intended as a science fiction question, but an actual science ...
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1answer
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Wormholes man made are real? [closed]

Can we bend two points of spacetime in a way we would create a wormhole ?Why havent we tried it yet?How much energy would we need to do it?
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2answers
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If I could see from a Gravitational-Time dilated place to somewhere far which is not dilated, would I see fast moving people?

Gravitational time dilation like the one shown in the movie Interstellar, causes time to move slowly for someone within the high gravity reference frame. Now let's say that from such a place, I was ...
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4answers
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Why do things float in space, though the gravity of our star is always present? [closed]

In the solar system, things float around. We are so certain that the gravity of our sun exists. Still, why does that gravity not influence satellites and other objects there? Our solar system is also ...
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Why can't we feel the Earth's revolution?

I googled it and checked a few Q&A and there's only things about "Earth's rotation". But why can't we feel the revolution? They say we can't feel the rotation because the Earth spins at a ...
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1answer
66 views

If a solar system were surrounded by a cloud of debris, is it possible for a planet's orbit to intersect it?

I'm doing research for a story that I'm writing and I'd like some physics advice on whether a hypothetical system of celestial bodies is possible. Suppose the following: A system of planets orbiting ...
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3answers
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Can a magnetic field of an object be stronger than its gravity?

Can a planet, star or otherwise have a magnetic field that is stronger or have more range than its gravity?
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If a massive object like Jupiter flew past the Earth how close would it need to come to pull people off of the surface?

I understand this is a silly hypothetical but I'm asking for a 7 year old so please bear with me. Imagine an interstellar stray gas giant comes flying through our solar system. If we were not ...
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3answers
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Can a black hole “supernova”?

In layman terms: nothing ever escapes the pull of a black hole, not even light when a super massive star reaches the end of it's life you get a supernova sometimes the "remains" of these stars can ...
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Planets may repel each other in few cases

We know that when two huge black holes collide they produces gravitational waves in space time curvature. So if I am not wrong another object in space if goes in that direction during production of ...
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Are black holes spherical during merger?

I've been thinking about black holes, specifically during the final moments before two merge. I'm wondering if black holes, or I guess more specifically their event horizons, are always spherical. ...
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A quantitive estimate of the size above which celestial bodies must be near-spherical [duplicate]

Asteroids and smaller celestial objects tend to be odd-shaped, whereas planets are always spherical (or slightly oblate due to their spin). The reason obviously is that for sufficiently large masses/...
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3answers
168 views

Do photons slow down as they approach the event horizon of a black hole?

So, if a black hole is so dense, that light cannot escape, what happens to the photons as the approach and go past the event horizon (or some other horizon, about which I am ignorant)? Do photons ...
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Does time dilation at the event horizon prevent us from seeing any changes?

If gravity is so strong at event horizon as we assume, and thus time dilation makes time infinitely slow for us, the distant observers, how could we ever observe any events ocurring over time? Wouldn'...
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As matter approaches a black hole, does it speed up?

If so, how do we know it speeds up? Doesn't time slow down as gravity increases? If time slows down around a black hole, is it possible matter doesn't actually speed up?
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1answer
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Is the gravity on Kepler 39b higher than on the Sun?

According to the formula for gravitational acceleration $a = GM/r^2$ where $G=6.674 \times 10^{-11}$, Jupiter with mass 1.89813 × 10^27 kg and radius 69,911,000 m gives a gravity around 25m/s^2. The ...
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If a photon were 1 Planck length away from the event horizon of a blackhole, would it be able to escape the blackhole's gravitational pull?

I understand that one could theoretically replace the sun with a blackhole without affecting the orbits of the planets. This leads me to believe that a blackhole isn't a "cosmic vacuum cleaner" so ...
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1answer
40 views

Mass of Photon and Black holes [duplicate]

The gravity caused by a black hole is said to be so strong such that even light(photons) can not escape from it. since gravity exist only in between objects with mass, How does a black hole attract a ...
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1answer
165 views

How to determine the mass of a galaxy?

I am having a slight disagreement with my professor. We can measure the mass of a distant star cluster from: A.Its color B.Its radius C.Its metallicity D.Smearing of lines in ...
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3answers
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Can't pulsars and stars be used for gravitational wave measurement?

Suppose that we collected photons from a distant star, and they arrive regularly at 15 photons every microsecond onto a CCD, when a gravity wave bends space time, wouldn't the regular 15 photons graph ...
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3answers
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Why do astronauts move so slowly in zero gravity? [closed]

When astronauts are floating about in a spaceship or space station, they nearly always move very slowly. After doing a bit of research I can't see why being in zero gravity would restrict movement to ...
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1answer
85 views

Looking at the Expanding Universe through the lens of relativity [closed]

The basis and most observable metric for how the universe is understood to be expanding at an accelerating rate is the red shift in observable light. I am assuming it has been thought about or maybe ...
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1answer
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Why does gravity make time go slower and warp light?

I know that objects with lots of gravity are capable of warping light or slowing time (an example being a black hole). I also know this is because of the theory of relativity, but I need someone to ...
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2answers
161 views

A neutron star without a flat surface and an atmosphere?

In the Kurzgesagt video Atoms As Big As Mountains — Neutron Stars Explained they state that neutron stars have an atmosphere that reaches about 10 centimeters above the surface. How is this possible?...
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1answer
41 views

Mini disk of a blackhole meaning

What is meant by the "mini disk" of a blackhole? Is it the same as accretion disk? If not, whats the difference? Eg: In the abstract of this paper https://arxiv.org/abs/1806.05697 it is mentioned "...
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1answer
244 views

Is the moon inside earth’s atmosphere? If so, what are the consequences?

Recently, a paper was published claiming that the Earth’s atmosphere extends far beyond the Moon. This has been reported on by a number of news sources and websites, including the ESA, Business ...
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1answer
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Can the moon's gravity influence be observed on the space station's orbit?

In browsing through Astronomy Stack Exchange, I came across this question about orbiting the moon (Is it possible to achieve a stable "lunarstationary" orbit around the moon?). In further ...
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1answer
126 views

First observation that the movement of a planet or asteroid in its orbit was affected by another planet?

Answers to the question How did Kepler determine the orbital period of Mars? describing careful observations centuries ago got me thinking. Question: What was the first analysis of observations that ...
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1answer
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How to separate binary and optical stellar pairs?

I have list of stellar pairs from The Washington Double Star Catalog (WDS), i.e. I have next parameters: angular separations position angles stellar magnitudes of both components Additionally I have ...
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2answers
164 views

Is gravitational lensing a good way to search for negative mass?

Is it possible to verify negative mass with gravitational lensing? The following video proposes an idea that galaxies are surrounded by negative mass: https://youtu.be/MZtS7cBMIc4 Could this be ...
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3answers
644 views

Why do sun spots appear near the equator of the Sun?

I noticed on many examples sun spots are near the equator of the Sun. Why are there no sun spots closer to the poles of the Sun?
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3answers
444 views

Can two planets in an empty universe meet/be pulled together?

For this question assume that the entire universe is completely empty. The universe is not expanding or contracting, it is completely motionless since time immemorial and has never moved before. Only ...