# Questions tagged [newtonian-gravity]

Questions regarding the theory of gravity as proposed by Newton, in which the force of gravity depends only on the mass of bodies, a constant, and the distance between them, and depends on one equation.

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### Does Mach's Principle imply the Newtonian constant of Gravitation or the speed of light (or both) change with time as the Universe expands?

In his 1999 book Relational Mechanics Professor Andre K. T. Assis gives an equation on page 180 (Equation 8.37) for the Newtonian constant of gravitation, $G$, that he has arrived at heuristically, ...
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### Gravitational waves vs. "normal gravity"

Imagine you have a super sensitive 3D accelerometer/gravimeter alongside the Virgo interferometer. A gravitational wave passes by and Virgo detects a variation in the length of the 3000m long arms. ...
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Confusing title, I know. Imagine a perfect, homogenous sphere with an exact radius of $1,000 \text{km}$ and an exact mass of $8 \times 10^{15} \text{kg}$. If you use the formula for escape velocity $... • 2,699 5 votes 3 answers 268 views ### Are there really confined Globular Clusters? I am trying to find real physical examples of (self-gravitating) astrophysical systems that are appropriately confined and can thus be seen as in equilibrium. Modelling-wise, you can theoretically put ... 17 votes 4 answers 4k views ### What is the shape of orbit assuming gravity does not depend on distance? We know that the orbit of the earth is elliptical considering the force of gravity is inversely proportional to the square of the distance. But assume that, gravity does not depend on distance. ... • 171 1 vote 0 answers 24 views ### How can Aggregation of Gravitational Fields of subplanetary solar objects improve our understanding of the motion of the planets? If we imagine magnets on a table as a simplified analogy in regards to gravitational attraction between objects, then it may be demonstrated that when three objects are placed in a row labeled in ... • 11 0 votes 0 answers 39 views ### Lagrange points and Laplace equation boundary condition I have been reading about Lagrange points and Lagrange regions and how we can apply Laplace's equation for these regions however which are the boundary conditions of the Laplace equation at these ... • 111 2 votes 2 answers 170 views ### Does MOND change general relativity? Newton's inverse square law appears in General relativity for small masses . Since MOND uses 1/radius instead of 1/radius squared has General relativity been modified to accommodate this? 1 vote 0 answers 54 views ### Are short-period comets more stable (in their orbits) than long-period ones? Why the sharp distinction between short-period (P) comets of less-than-200-year orbits and those (C) with even slightly longer ones? To explore the possibility that it has to do with stability, I will ... • 5,177 -1 votes 1 answer 93 views ### If 16 million kilometers were added to Earth's semi-major axis, what measurable effect would there be on Mars' orbit? I have some education in astronomy, but nothing extensive in astrophysics. I can follow mathematical procedure with assistance. Procedural responses are most welcome! • 171 4 votes 1 answer 254 views ### How can Deep MOND regime apply inside a star? MY UNDERSTANDING OF THE MOND THEORY As I understand it, Milgrom's MOND model can be interpreted in one way by saying that Newton's Law of Gravitation on its own is insufficient to predict the ... • 1,444 1 vote 0 answers 130 views ### In between Classical Gravitational Deflection (2GM/rv^2) and General Relativity (4GM/rc^2) While researching online I've found two expressions for the angle of deflection by gravitational lensing:$\dfrac{2GM}{rv^2},$Classical(Newtonian) prediction$\dfrac{4GM}{rc^2},$Relativistic ... 5 votes 1 answer 115 views ### Is an extreme precession on a tidally locked planet possible? Let's assume an exoplanet orbits a red dwarf star closely enough that is tidally locked to it. Is it possible for the planet to have a significant axial precession? If not naturally, is it possible to ... • 53 2 votes 2 answers 202 views ### At what distance does MOND Modified Newtonian Dynamics take effect? At what distance does MOND Modified Newtonian Dynamics take effect? I understand MOND is described in relation to very slow accelerations, which is related to distance. It is mentioned it has an ... 0 votes 2 answers 396 views ### How is light unable to escape a black hole if photons are massless? [duplicate] I understand light will follow the curved space that the BH is causing due to its mass. I also understand that mass attracts other mass but then photons are massless. So 0(photon) x m2 (the BH) is ... 1 vote 1 answer 80 views ### How will be changed Hill's radius and Kepler's formulas in case of 2D space instead of 3D? Imagine that Flatland habitats go into space. All stars and planets are the circles instead of spheres and gravity law is$F=Gm_1m_2/R$instead of$F=Gm_1m_2/R^2$. How the other formulas will be ... • 256 13 votes 2 answers 4k views ### Why do gravitational waves travel "only" at the speed of light but the gravitational scalar potential is instantaneous? To my old Space SE question Besides retarded gravitation, anything else to worry about when calculating MU69's orbit from scratch? @DavidHammen's excellent answer replies that one should not add a ... • 30.7k 1 vote 0 answers 31 views ### Virgin Galactic's and Blue Origin's Space Flights - are these just Extended Skydiving in an Enclosure? [closed] Sorry for three questions in the three paragraphs below, but they all are around the same curiosity that I have. In both of Virgin Galactic and Blue Origin's space flights happening in July 2021, it ... • 11 19 votes 4 answers 6k views ### Can Newton's gravity equation explain why black holes are so strong? I was just wondering why black hole's gravitational forces are so powerful. I know it's usually explained by Einstein's relativity which states that when an object becomes infinitely dense (a compact ... • 655 0 votes 1 answer 97 views ### Non-keplerian orbit features of orbits in uniform mass distribution For the first Kepler's law the orbit of a planet is an ellipse, with the Sun in one of the foci, but I've read that in the case of an homogeneous sphere distribution, orbits can be elliptic, but the ... • 21 3 votes 1 answer 112 views ### Virial ratio behaviour I think I didn't understand something about virial theorem for an$N$-body system, for instance the behaviour of virial ratio$T/\Omega$, with$T$kinetic energy and$\Omega$gravitational potential ... • 43 2 votes 1 answer 85 views ### In 'Modified gravity' theories like MOND, are galaxies and stars actually, slowly accelerating? In the normal sense? In the Modified Theory of Newtonian Gravity or MOND, they say that massive objects, accelerating slowly, experience this modified gravity. But are they actually gaining in velocity, albeit very slowly?... • 5,177 3 votes 0 answers 119 views ### Gravity on Mercury's highest elevation? This post answers what is Mars' gravity at its highest point (Olympus Mons) compared to the Earth's and Mars' standard, it's 0.3736 g (Mars standard is 0.3794 g). This also seems to be the lowest ... • 113 18 votes 3 answers 6k views ### Intuition about why gravity is inversely proportional to exactly square of distance between objects What is the intuition behind why gravity is inversely proportional to exactly square of distance between two object and not cube or not some multiplier. Basically how Newton came up that its exactly ... • 322 1 vote 2 answers 546 views ### Considering that the moon’s gravitational pull on earth is so weak- we need special instruments to detect it- how does it cause the tides? That the moon’s gravitational pull is responsible for the tides is established. However, if we want to detect the moon’s gravitational pull on earth, this is very challenging. This seems to be a ... • 19 2 votes 0 answers 62 views ### Can tidal locking increase rotational kinetic energy? Where does the energy come from then? [closed] I was thinking about the explanation for how the Moon gets tidally locked with the Earth. We are working in the non-rotating reference frame of the Earth, and assume it is inertial (to an approximate ... 4 votes 2 answers 1k views ### What is the minimum mass of a celestial object so that it can have a moon? I was wondering how massive something have to be so that it it can attract moons by pop culture standards (ellipsoid/round shape). Could a planetoid have a moon? What is the relation between the mass ... • 311 8 votes 1 answer 1k views ### How strong are the tides raised by Io on Jupiter relative to the ones raised by the Moon on Earth? There seems to be 2 ways of calculating tidal forces that appear contradictory. Either: By calculating the difference of Io's gravitational acceleration on a point on Jupiter's near side and the ... • 968 4 votes 1 answer 193 views ### Does the gravitational attraction near the surface of dense celestial objects diverge from inverse square? Does the gravitational attraction near the surface of dense celestial objects (neutron star, white dwarf itc) diverge (to infinity) from inverse square? This question is inspired by the similarity ... • 73 4 votes 1 answer 258 views ### Why does Newtonian physics give the right radius for a black hole? When computing the distance at which the escape velocity is equal to the speed of light, the result is equal to the Schwarzschild radius. Is this just a coincidence, or is there a physical reason why ... • 17.6k 4 votes 0 answers 98 views ### Gravitational Slingshot If a spacecraft slingshots around a planet P (with escape velocity V) at an angle$\theta$, I understand that the resulting velocity is$${ v }_{ 2 }=({ v }_{ 1 }+2u)\sqrt { 1-\frac { 4u{ v }_{ 1 }(1-... • 141 1 vote 1 answer 128 views ### Could a gas giant orbit a star with a 30 year period at a distance of just 1 AU? Assuming a star with similar properties to our sun, could a gas giant orbit it with an orbital period similar to that of Saturn, but, at a much closer orbital distance, more similar to 1 AU? • 19 2 votes 0 answers 121 views ### Freefall timescale for a Jeans-unstable hydrogen cloud of mass M I'm working on a project (personal, not academic) that involves calculating the collapse timescales for protostars which will end up becoming stars of varying given masses. I'm treating the pre-main ... 7 votes 3 answers 2k views ### Gravitational acceleration inside a planet The gravitational acceleration, g, inside the Earth generally decreases with decreasing distance to the center: However, apparently for Jupiter, the gravitational acceleration only increases with ... • 357 3 votes 1 answer 151 views ### Can gravity be amplified by other celestial bodies in its vicinity? I`m wondering if the gravitational pull from earth that should be constant around the planet, will get amplified by a celestial body like the moon orbiting the earth? • 85 1 vote 2 answers 610 views ### Universe Sandbox 2 accurate representation of gravity I've been playing Universe Sandbox for a while now and I have never been able to make a near Earth asteroid collide with it. By "make" I mean, simulating billions of years of known, near Earth objects ... • 113 2 votes 0 answers 812 views ### Gravity on a right rectangular prism? [closed] Let's assume there is a right rectangular prism floating about in space, what would the gravity be like across its 6 flat surfaces? What gravity would you experience if you set foot on the rectangular ... 3 votes 2 answers 206 views ### Gravitational attraction of Sun on distant object A hypothetical situation which will help me with a real-life problem. Several stationary objects are placed at great distances from our Sun -- say 0.1 light year, 0.5 ly, 1.0 ly. Assuming no other ... • 41 1 vote 1 answer 1k views ### Equations of motion for Earth and Moon One of the simplest versions of Newton's equations of motion for the Sun, Earth and Moon can be obtained by making the approximation that the three bodies are perfect spheres. In this approximation, ... • 161 1 vote 1 answer 232 views ### Is it true that open clusters have$E > 0$and globular clusters have$E < 0\$?

I just need to confirm or refute something I'm believing since a very long time, maybe without real evidence. Can we distinguish stellar clusters by their total mechanical energy ? Is it true that ...
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### Natural units of star clusters angular momentum and energy

I'm calculating the total angular momentum of a bunch of theoretical stars of a few solar masses, separated by a few light years, moving at velocities of about a few dozens of km / sec. Mechanical ...
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### Orbits using Newtons laws

I am making a small orbit simulator. I figured out Kepler's laws and know how to work with them to "update" an orbit based on time. So now I want to know how I can describe orbits with newton laws. ...
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### Could the Sun's bending of light be measured on photographic plates before Einstein's prediction?

It was predicted from Newtonian physics already in the 18th century that gravity should bend light, but not by as much as general relativity predicts. This was first confirmed during a solar eclipse ...
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### Parabolic or hyperbolic trajectories

According to Newton's laws, the trajectories for the two-body problem are conics: either ellipses, or parabolas or hyperbolas. Of course periodic motions require Ellipses and in the Solar system these ...
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Question: Approximately once in 5 years people on Earth can observe bright comets whose nuclei have radius about 1km. The orbits of such comets are close to parabolic. Assuming that these nuclei are ...
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### Precision of geocentric gravitational constant

I am looking for an answer as to why the geocentric gravitational constant, μ, defined as the product of the gravitational constant, G, and the mass of a body (earth in this case), M, can be ...
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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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### 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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### What's the relation between Einstein's Gravitational Theory and Dark Matter?

I was reading an elementary book on dark matter (in fact, a historical perspective) and there were mentioned how the scientific community react to the idea of dark matter proposed as a solution to ...
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