All Questions
Tagged with newtonian-gravity planets
311
questions
4
votes
4
answers
343
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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
78
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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
82
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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 ...
- 533
1
vote
4
answers
160
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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
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votes
1
answer
21
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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 ...
- 69
0
votes
2
answers
65
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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
5
votes
2
answers
289
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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
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2
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98
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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 ...
- 5,148
0
votes
4
answers
110
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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
4
votes
2
answers
326
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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 ...
- 6,112
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0
answers
42
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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
59
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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 ...
- 866
0
votes
0
answers
44
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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
1
answer
61
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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
1
answer
75
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Potential energy with different heights [duplicate]
If system consists of earth and ball and ball is dropped from height $h_i$ to $h_f$, then:
$\Delta U = -(W_{earth} + W_{ball})$ ($W_{ball}$ can be neglected since it's small)
$\Delta U = -(-mg(h_f - ...
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votes
0
answers
69
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Dynamic equilibrium of planets
We can describe statical equilibrium ( forces, moments ) in a cuboid $$ \Sigma F_x=0,\Sigma F_y=0,\Sigma F_z=0~$$ In dynamics can we describe similar dynamic equilibrium within an inertial ...
- 1,032
2
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1
answer
1k
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What does Newton's Theorem XXXIII in his book "Principia" mean?
If to the several points of a given sphere there tend equal centripetal forces decreasing in a duplicate ratio of the distances from the points; I say, that a corpuscle placed within the sphere is ...
- 870
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2
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795
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How would the volume of a drop of water (from a dropper) on the Moon and other bodies compare to one on Earth? (indoors of course!)
Searching for "volume of a drop of water from an eyedropper", I ran across this answer on Quora:
It depends on the size of the dispensing tip, but generally for a Pasteur pipette it is ...
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8
votes
5
answers
290
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What is the gravity in the center of Earth?
Let's suppose the earth is a perfect sphere and let's ignore its rotation and movement.
What would happen if I would be in the center of the earth? Would the gravity be zero in any direction so I ...
- 209
1
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2
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47
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Is it possible to determine if a planet can have a moon based on its mass and gravitational pull?
I'm curious, if based on what we know with Newton's law, can we determine if a random planet, knowing it's mass and gravitational pull, can hold a moon in it's orbit.
Or to phrase it another way, is ...
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3
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345
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If the Earth rotated slower about its axis, would your apparent weight increase or decrease?
The title above was a question on an exam that was marked wrong for me. I answered that if the Earth rotated slower (i.e. longer days), my apparent weight would increase. I based this on the ...
- 135
2
votes
1
answer
69
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On the tidal heating of a moon. What is the second Love number?
Years ago it was asked here how to calculate the tidal heating of a moon orbiting another body with a simple equation. The answer is very detailed. They explain the equation, its shortcomings, the ...
2
votes
2
answers
356
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Is $F=mg$ derived from Newton's law of universal gravitation $F=Gm_1m_2/r^2$?
If so, that means gravity is only 9.8 m/s^2 at the surface of the earth?
- 21
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votes
1
answer
92
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Change in $g$ effective due to rotation
$g$ effective at any latitude changes due to rotation of earth. Does it also change due to rotation when the body is at height or at depth or does it change only at the surface?
Edit: I am referring ...
- 69
1
vote
2
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377
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Correct explanation of tides [duplicate]
In the explanation of tides on earth there seem to be different versions for the second water bulge on the side opposite to the moon, while everybody seems to agree that the bulge on the moon side is ...
- 4,292
14
votes
9
answers
7k
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Is Earth really flattened at the poles because of centrifugal force?
My question is pretty much all in the title. I was always told that our planet is flattened at its poles due to the centrifugal force generated by its own rotation. However I don’t see how centrifugal ...
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1
answer
78
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How does a gas giant planet hold it's spherical shape when it has tidally locked rotation in it's orbit around the Sun?
How does a gas giant planet hold its spherical shape when it has a tidally locked rotation in its orbit around its Sun? Wouldn't it fall apart without its gravitational pull from the rotation? How ...
6
votes
2
answers
2k
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Possible non-negligible physical effects that relate planetary/lunar geometry and seismic activity such as earthquakes?
Could any forces from the moon, the planets or the sun in orbit hypothetically influence seismic events on earth? And if yes how to approximately calculate and compare the magnitude of the forces?
...
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2
votes
1
answer
77
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Falling at the centre of the Earth
Let’s assume to drill a hole at Earth surface at the point P1. The hole passes throughout the centre of the Earth and finishes at the opposite side at the point P2. Let’s assume then that 1) Earth ...
- 566
1
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0
answers
41
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Did Newton derive Titius-Bode Law of the planets in his Principia? [closed]
In college I was taught that no one knows why the planetary orbits conform to the Titius-Bode Law.
Recently I read that Newton HAD figured that out in his Principia.
Right Now I can’t even find a ...
- 11
0
votes
1
answer
18
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Physics of a falling body within a spherically uniform system [duplicate]
I was reading The First Three Minutes and in the book it talked about how if a stone fell in a cave deep in the Earth we could calculate it's motion as if the surface of the Earth is the surface of ...
- 38
2
votes
0
answers
64
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Most stable shape if Newtonian gravity was proportional to $r^\alpha$
Consider lots of mass in isolated 3D space, close to each other. Consider that only the gravitational force (Newtonian) exists. Also consider that there is no rotational motion.
It is evident that a ...
- 221
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votes
1
answer
57
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Gravity train in other planets?
A Gravity train (https://en.wikipedia.org/wiki/Gravity_train) goes through a tunnel inside a planet that connects point A with point B. On Earth, the train would not gain enough impulse to reach the ...
- 2,462
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3
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262
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Does gravity cause the Earth's equatorial bulge?
The way I understand centrifugal force, I don't see how Earth's daily rotation alone would cause equatorial bulges to form. The usual explanation is that the centrifugal force increases with distance ...
- 31
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votes
2
answers
106
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What force accounts for Earth's equatorial bulge in an inertial frame of reference?
I am confused as to how Earth's centrifugal effects from its daily spin can be explained from an inertial frame of reference relative to the distant stars. The usual explanation is that the ...
- 31
2
votes
1
answer
290
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What is the rate of change of the Moon's eccentricity?
So I know the Moon's current average eccentricity is ϵ≈0.039±0.006, but was this always the case? Was it ever increasing or decreasing, and if so is it known what the current rate of change is for it? ...
- 161
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votes
0
answers
43
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Why are the orbit of planets usually ellipses? [duplicate]
There has been a similar question about planets' orbits being ellipses but the answer circulates around how the circle is a special type of orbit which doesn't really answer my question.
Elaborate ...
- 159
2
votes
1
answer
59
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Gravitational Potential of a Slowly Spinning Planet
I'm working on a problem in Thorne & Blandford's Modern Classical Physics regarding the shape of a constant density, spinning planet (Exercise 13.5). It asks you to argue that the gravitational ...
0
votes
2
answers
3k
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Gravitational potential energy inside of a solid sphere [duplicate]
I am self-studying classical mechanics. I came across a problem which required me to calculate the gravitational potential inside of a sphere. I found in one of my textbooks that the potential energy ...
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0
votes
2
answers
47
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Lopsided planet
Something that has always puzzled me about Pangaea.
If we have a "roughly" spherical mass of solids, aren't two points on opposite sides approximately the same distance from the center of ...
- 369
2
votes
2
answers
146
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A simple proof that under Newtonian gravity rotating massive bodies are ellipsoids?
Here is my attempt at deriving the shape of an idealized rotating massive body under Newtonian gravity, assuming that the gravity force points towards the center of mass and shape of the body is ...
- 513
1
vote
4
answers
94
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A problem Understanding how a two-body system of planets starts rotating around barycentre
Consider,We are Creating a Two-body system in free space,Where no other mass exists,Let's Take First Mass M1 and hold it,Now bring Second Mass M2,hold it up,Now we are giving a suddenly impulse To M1 ...
- 452
1
vote
1
answer
88
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What would happen if the Earth rotated at the rate required to achieve orbit at its radius? I.e ~7k m/s instead of ~460 m/s
To achieve a circular orbit, you need to have a velocity of $$v = \sqrt{Gm/r}$$ which is about 7 km/s at the Earth’s radius, but the Earth’s rotational speed is only about 460 m/s (by taking the ...
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votes
3
answers
712
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Would it be possible to ride a bicycle on the surface of Mars?
Could you ride a standard bicycle on the surface of mars?
Assumptions:
You are wearing a suit to provide life-support
You are riding on a prepared smooth flat martian 'road'
If you were to ride ...
-2
votes
3
answers
149
views
Why is the shape of the orbit of the Earth as it is?
My View: I think that if the sun were only force acting on earth (as a centripetal force), the earth would have a circular orbit. Since other planets also exist , there also exists gravitational force ...
- 159
3
votes
2
answers
175
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On a Torus World and the force upon inhabitants
I am looking into torus worlds for fiction, and I know how to calculate the necessary speed to rotate, and necessary radius, for such a world to get a specific force of gravity.
But what I am ...
- 221
4
votes
1
answer
2k
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Newtonian contribution to perihelion precession of Mercury
We have seen that the orbits of the planets around the sun can be
found, to a good approximation, by only considering a two-body system
(a planet and the sun) interacting through a central force. ...
- 717
1
vote
1
answer
71
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How do we find the centripetal forces of 3 planets revolving around a point given that they have the same mass?
Let's say we have three planets revolving around a point. We know that the force of gravity acting on all of these planets can be taken from $g = G{m_1m_2 \over r^2}$. We can derive the velocity of ...
0
votes
1
answer
121
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Body falling through Earth
Imagine a body with mass $m$ moves through a pipe through the centre of earth. The gravitational force is given by $\vec{F}=-C \vec{r}$ where $C$ is constant. I want to determine the 1D equation of ...
- 15
1
vote
2
answers
267
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How close can Jupiter be to Earth without making Earth unhabitable? [closed]
How close can Jupiter be to Earth without making Earth unhabitable? What's the closest distance possible? Can Jupiter be twice or three or four times as close to Earth as Mars without having any ...
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