All Questions
1,041 questions
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Can the rotation of the liquid layer of the core around the solid core stop a planet's overall spin rotation?
In some planets like Earth or Jupiter there is an external liquid or molten layer of the core which rotates around a more deeper solid core (partly due to the planet's spin itself). This dynamo effect ...
- 2,878
0
votes
0
answers
21
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Maintaining the magnetic field in gas giants in the future?
Let's set a planetary system similar to the Solar system in the far future, where the gas giants have cooled down significantly.
Eventually, would the fluid metallic hydrogen layer solidify?
And if it ...
- 2,878
0
votes
0
answers
67
views
Existence of hollow planets
Recently I read a sci-fi describing a species living in a closed hollow space in a planet. An earlier answer suggested that such structures could exist but will not be stable, if only effected by self ...
- 251
0
votes
3
answers
83
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What if the Earth lost its gravitational force? [closed]
It's common to find such questions in textbooks, and generally the answer is that in the absence of other external forces (such as gravitational forces due to other stars and planets) a person ...
3
votes
1
answer
88
views
Toroidal planets to toroidal black holes -- what changes?
It's believed that a sufficiently quickly rotating planet-sized mass could be stable in a toroidal planet formation (though vanishingly unlikely to form naturally). However, assuming no cosmological ...
0
votes
1
answer
53
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Clockwise tornados in the southern hemisphere
When water is flushed out from a kitchen sink or a toilet in the northern hemisphere an anticlockwise swirling vortex is seen due to the action of the Coriolis force. It appears to be the case even ...
- 1,094
2
votes
1
answer
223
views
Does the orbital plane that contains the trajectories of 2 bodies pass through the center of mass of each of the bodies?
Two bodies that attract each other gravitationally will move in a conic trajectory with respect to the center of mass of both. A conic is the meeting of a cone and a plane thus it is always a plane ...
- 177
16
votes
3
answers
4k
views
Neil Tyson: gravity is the same everywhere on the geoid
Tyson claims our weight is the same at the North Pole as it is at the equator: Link. That the equatorial bulge lying outside a spherical shape doesn't exert gravity.
I'm pretty sure this is wrong but ...
- 486
5
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3
answers
307
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How would I calculate the gravity at a given depth on a planet with two distinct layers with different densities?
If you assume a planet to be one density then gravity just scales linearly from the centre to the surface, and you can use the surface gravity equation.
How would you go about working out the gravity ...
- 153
1
vote
4
answers
177
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Does moving from the equator to a pole require more or less energy (work) than moving from a pole to the equator?
Let's assume the earth is perfectly smooth, and there are no other effects of gravity from other bodies such as the sun or moon.
When the Earth rotates, centrifugal forces result in a 'bulge' at the ...
- 111
1
vote
1
answer
111
views
What is the cause for the acceleration of Earth?
I've read that spacetime curvature is present wherever initially parallel geodesics converge or diverge, and also that mass causes spacetime to curve. If there is indeed spacetime curvature due to the ...
- 13
0
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0
answers
24
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How can I calculate the heat transfers caused in Venus's atmosphere by a stellaser?
In Isaac Arthur's video Winter on Venus, he discusses using a stellaser to heat Venus’s atmosphere and remove its gases, but he doesn't go into much detail about the heat transfer involved in it.
The ...
- 101
1
vote
1
answer
67
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Problem understanding the bending of space-time curve as gravitational force! [duplicate]
I got the point of considering gravitational force as curvature on space-time fabric for bigger objects like stars, planets, blackholes. But my doubt is over the objects like us, what keeps us on this ...
0
votes
3
answers
908
views
What counts as the Earth's mass? At which point would it increase or decrease?
I get that gravity depends on the mass of an object: more mass = higher gravity. But over time humans have been doing stuff to the total amount of stuff on the Earth due to space travel. At which ...
- 123
1
vote
1
answer
46
views
Is it possible to charge a zero potential ball?
I've been studying electrostatic potential and capacitance and am curious about the Earth's role in absorbing charge. The Earth is often considered an almost neutral body that can absorb an unlimited ...
- 13
0
votes
2
answers
64
views
Components of Earth's angular velocity when vertical axis is aligned with apparent gravity
I've been reading the book "Classical Mechanics" by John Taylor, and in the chapter about noninertial reference frames, it states that the direction of $g$ (the apparent gravity, which ...
- 101
1
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0
answers
66
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Numerical Solution of the circular restricted three body problem [closed]
I am trying to numerically solve the differential equations in the planar circular restricted three-body problem. In the rotating frame, the differential equations are given by
\begin{equation}
\...
- 35
1
vote
0
answers
66
views
Why does a moon's orbit get more circular with time?
I understand that there is a transfer of energy between a moon and a planet depending on whether the moon is orbiting faster or slower than the spin rate of the planet. This would obviously change the ...
- 257
4
votes
4
answers
523
views
What is the relationship between gravitation, centripetal and centrifugal force on the Earth?
I'm trying to analyze a situation wherein a ship is moving across the surface of the earth. I am trying to analyze this situation in a reference frame that is rotating with the earth (NED frame).
I am ...
- 311
1
vote
2
answers
87
views
The topology of planets [duplicate]
Just a curiosity:
Let $g \in \mathbb{Z}_{>0}$. Is it possible for a planet of topological genus $g$ to exist? For example, is there any contradiction (from the point of view of physics) in assuming ...
- 121
0
votes
2
answers
88
views
Why are planets denser as you approach the center?
Gauss' law says that the net electric force inside a hollow, uniform, not rotating sphere is zero. Since gravity is also proportional to the inverse square of the distance, I assume this should apply ...
- 545
1
vote
4
answers
170
views
Gravitational attraction between two bodies
While the gravitational force between two bodies is directly proportional to their masses, and inversely proportional to the distance between them is understandable / seems logical, how did Newton ...
- 123
0
votes
1
answer
27
views
Can we treat the entire mass of the spheroid as being concentrated at its center?
I know that to find the gravitational force between two objects, if either of them is a sphere, we can assume its mass to be concentrated at its center and use the formula for gravitational forces for ...
- 79
0
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0
answers
51
views
Despite tides the Moon, as far as I know, doesn't slow down. Where does the energy come from? [duplicate]
Hy, I don't have anything to do with physics, so please forgive me if I explain my question in a weird way ;)
As the Moon rotates around the earth it is creating tides and waves on the earth. IE it's ...
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19
votes
6
answers
9k
views
If gravity is not a force, what makes massive objects spheroid?
For most of my life, the explanation given for why celestial bodies like stars, planets, etc. are round is due to gravitational force. Simply put, if an object has enough mass, it will, in turn, have ...
- 413
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2
answers
65
views
Why are planets cold?
Excuse me for me ignorance, I'm just fiddling around this question for quite a while.
The question of course is not limited to planets. Boiling down to, why isn't the universe heated up by now to ...
- 101
0
votes
2
answers
72
views
How symmetric do we know the gravitation field to be?
Currently, the only ways to measure gravity is on quite large scale. So these experiments measure gravity averaged between vast systems of particles. Of course, such an averaging results¹⁾ in a ...
- 101
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votes
1
answer
112
views
Minimum size for a planet to have a molten core
What would be the minimum size for a planet or moon so that it would have a molten core? Gravity and density would play a part but how could this be worked out?
- 319
0
votes
0
answers
69
views
Magnetic compass working on the Moon and the Mars planet
Mars planet
Moon
Magnetic compass
Theoretically and practically, will a magnetic compass work on the Moon and the Mars planet?
- 111
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votes
2
answers
77
views
What regulates the size of our atmosphere?
Our atmosphere is only about 100km thick before the official start of space. That is a mere 1.57307% of the radius of Earth (6,357km). The difference between the gratitational force at sea level and ...
- 413
4
votes
1
answer
394
views
What are the odds of a rogue planet that enters into a galaxy reaching the black hole at the center of the galaxy?
I am wondering if anybody has ever calculated the odds of a rogue planet, which has been traveling through interstellar space and then enters into a galaxy, being able to travel all the way to the ...
user300400
5
votes
2
answers
307
views
Helium in Uranus atmosphere
I read that in 1986 Voyager 2 measured the composition of Uranus' atmosphere, which turned out to be composed of $85 \%$ hydrogen and $15 \%$ helium.
It's not clear to me how this relevant amount of ...
- 566
1
vote
2
answers
194
views
How to calculate equilibrium height of tidal bulge?
I am trying to model the shape of the tidal bulge caused by the moon.
I asked GPT for a formula and it gave me equilibrium tidal bulge height as
$$\frac{2 R_{earth} G M_{moon}}{3 r^3 \Delta g}$$
and ...
- 5,188
0
votes
4
answers
155
views
What is the real shape of Earth? [duplicate]
As it now widely dicussed and accepted that Earth is not a 'perfectly round sphere/ball but more a 'oblate spheroid' why then do NASA have 'photographs' of a ROUND Earth?
- 11
2
votes
1
answer
64
views
Angular momentum of the Moon (or any body orbiting another orbiting body)
Let the Moon have angular velocity $\omega$ around the Earth. The Earth itself revolves with velocity $V$ around the Sun. The radius vectors are $r_i$ from Sun to a point on the Moon, $r_i'$ from ...
- 33
3
votes
2
answers
548
views
Is it possible, by monitoring the brightness of stars, to find a “copy of the Earth + Moon” near them?
More than a dozen Earth-like planets have been discovered around nearby stars based on observations of changes in the brightness of their sun as they pass across its disk (transit events). If an Earth-...
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7
votes
2
answers
505
views
Exact analytical solution for the surface gravity of an oblate spheroid
I would like to know if an exact solution for the surface gravity force components of an oblate spheroid has been published and if not can anyone derive it here?
Assume an ideal rigid oblate sphere of ...
- 10.1k
0
votes
0
answers
47
views
Why is Earth a sphere? [duplicate]
Physicists and Physics enthusiasts . I am new to this platform. And I wanted to post a question . Since I have nothing in my mind. I wanted to ask , Why is the earth a sphere and not other shape?
...
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votes
1
answer
72
views
What is the hydrostatic shape of an ideal rotating planet? [duplicate]
It is a well-known fact that rotating planets have a flattened spheroidal shape. However, the NASA site says about Haumea:
The fast spin distorts Haumea's shape, making this dwarf planet look like a ...
- 876
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votes
0
answers
36
views
Is either Geocentrism/Heliocentrism more "correct" than the other? [duplicate]
Yesterday there was a casual discussion of the findings of the scientist Galileo in my German class. It was mentioned that his breakthrough was that, he found a convincing explanation that earth ...
- 8,040
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0
answers
49
views
Why does a total solar eclipse happen every 18 Months?
What is the math involved in calculating how often a total solar eclipse happens. Can you predict it by just looking at the period of the moon around the earth and the period of the earth around the ...
- 1
1
vote
0
answers
34
views
Holsapple simple scaling law [closed]
Could someone explain Holsapple's simple scaling law?
Furthermore, is Holsapple simple scaling law able to be used on Earth in the context of dropping an object and measuring the impact crater size?
...
0
votes
1
answer
109
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Estimate Saturn's mass [closed]
How can you estimate Saturn's mass using data from Cassini's final moments in September 2017 (apoapsis on September 12 at 1:27 a.m. EDT Saturn time at a distance of about $1.3*10^6$ km from Saturn, ...
- 21
0
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0
answers
46
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Gravity formula inside a planetary core
I am trying to work through this problem so that I can understand how to convert from pressure values to radius values inside a planetary core in a code. The core has variable density depending on ...
0
votes
0
answers
18
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What is a simple way to estimate $σ_{RV}$ assuming photon noise in radial velocity measurements?
Hello there i have been trying to figure out what is wanted in the question "Simple way to estimate σ_RV assuming photon noise" for a presentation. But i can not seems to find much, but i ...
1
vote
1
answer
124
views
Atmosphere of a hypothetical planet
A hypothetical planet is 2/3 the radius of earth but has 1g surface gravity. Given the planet has the same surface gravity as earth, the atmospheric pressure would be the same. This would also mean ...
3
votes
0
answers
69
views
Why is sunset in mars blue?
This is the Martian sunset, as captured by the Spirit rover of NASA. Notice the colors are inverted, i.e. the direct rays blue and diffused rays red, which is exactly the opposite of what you would ...
- 12.6k
0
votes
1
answer
70
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Issue while understanding gravity/radius of earth graph [closed]
I have following question.
What are my opinions?
1. Option 1 - This is incorrect. I think dotted line in option 1 from bottom to peak represents center to surface of earth. After the peak, line ...
- 85
2
votes
0
answers
57
views
Would ocean tides on the moon of a gas giant really be kilometers high?
I was reading an article on exomoon habitability constrained by illumination and tidal heating. The article imagines an Earth-like exomoon around Jupiter-like host planet. That got me thinking about ...
- 21
4
votes
2
answers
341
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How to measure the ratio of a planet's radius to a star?
I was reading a physics problem related to astronomy, and upon re-reading it, I realized that it could be really indicated to extrapolate some really interesting physics-related information.
One of ...
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