48
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Can Newton's gravity equation explain why black holes are so strong?
No you can't and the behaviour of bodies with mass and of light is completely different near a compact, massive object if you use Newtonian physics rather than General Relativity.
In no particular ...
- 114k
42
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Intuition about why gravity is inversely proportional to exactly square of distance between objects
Imagine "gravity" spreading out in a sphere, like light from a bulb.
For each doubling of the distance, the sphere has four times the area. The surface area of the sphere is proportional to ...
- 87.6k
14
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Can Newton's gravity equation explain why black holes are so strong?
I am not an expert in physics and the explanation of the others is excellent. However, I noticed a flaw in your reasoning which they did not address.
You have written:
Considering the Newton's Law of ...
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10
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Gravitational acceleration inside a planet
You can use Gauss's law for gravitation to work out the gravity as a function of (interior) radius.
$$ \oint \vec{g} \cdot d\vec{A} = -4\pi G \int \rho\ dV\ .$$
What this means is that the flux of ...
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9
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Gravitational lensing in Newtonian physics
A photon is an entity defined in the context of a relativistic field theory, and so it doesn't really make sense to talk about the Newtonian bending of a photon. Necessarily, we need to substitute an ...
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How strong are the tides raised by Io on Jupiter relative to the ones raised by the Moon on Earth?
Both expressions are incorrect. The first should be
$$\frac{GM_{\text{moon}}}{(R_{\text{moon}}-r_{\text{planet}})^2} - \frac{GM_{\text{moon}}}{{R_{\text{moon}}}^2}\tag{1b}$$
or
$$\frac{GM_{\text{moon}}...
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9
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Can Newton's gravity equation explain why black holes are so strong?
While admiring @ProfRob's answer I'll add some additional perspective/background that may serve as a helpful stepping-stone since not every Astronomy SE reader is prepared to embrace General ...
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8
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Gravitational attraction of Sun on distant object
The full equation for the time for an object to drop is
$$t = \frac{ \arccos \Big( \sqrt{ \frac{x}{r} }\Big) + \sqrt{ \frac{x}{r} \ ( 1 - \frac{x}{r} ) } }{ \sqrt{ 2 \mu } } \, r^{3/2},$$
where $...
- 87.6k
7
votes
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Does one need to take into account finite gravity speed in N-body simulations?
If you're asking whether it's sufficient to use a retarded (time-delayed) positions to calculate gravitational forces, then no, that would be much worse than Newtonian gravity. For example, that would ...
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Orbits using Newtons laws
I like to classify solutions of the problem of the time evolution of the
complete initial state of a set of objects at some epoch time, where the
objects are subject to Newtonian gravitation into two ...
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7
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What is the minimum mass of a celestial object so that it can have a moon?
Planetoids can have moons and the minimum size is "pretty small". For example 2003 SS84is a small Near-Earth asteroid, with a diameter of 120m and a moon of about 60m in diameter, which ...
- 87.6k
6
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What is gravity really?
I can attempt to address the second part of your initial question (*"Is it a particle, a wave,...?") Einstein's theory of general relativity states that mass and energy bend space-time. Space-time, in ...
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6
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Can I measure the moon's gravity?
Running the math for a 5 meter long pendulum and 1 kg mass, I get an amplitude of 0,017 mm.
You are off by quite a bit. There is essentially no horizontal deflection when the Moon is at the horizon. ...
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6
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Does the gravitational attraction near the surface of dense celestial objects diverge from inverse square?
Leckner's paper deals with the effect of induced polarization on the spheres. Electrons are redistributed, making the force different from what one would expect. The gravitational counterpart is tidal ...
- 10.2k
5
votes
Gravitational lensing in Newtonian physics
Newtonian treatments of the bending of light go back to Laplace who, in 1798, wrote about light escaping from massive bodies, ie: black holes! See Appendix A of Hawking and Ellis "Large Scale ...
5
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Gravitational acceleration inside a planet
The short answer because Jupiter is a gas giant, so it's kind of got a very large atmosphere and atmosphere's aren't very dense. Also, if you look at your chart, the gravitation inside the Earth ...
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5
votes
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Virial ratio behaviour
The ratio $T/\Omega$ tells you about the acceleration of the system - or more specifically, the second derivative of its moment of inertia - it does not tell you about the velocity.
If the system ...
- 114k
5
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Can Newton's gravity equation explain why black holes are so strong?
If Einstein's GR equations are expanded in terms of familiar coordinates (Cartesian, spherical,...), the dominant or leading terms of the expansion (for the acceleration) can be written as the single ...
- 51
5
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Is an extreme precession on a tidally locked planet possible?
Yes.
Our own Moon is tidally locked to the Earth, but has an axial precession with a period of about 18.6 years. This precession is due to the 1.5 degree offset angle between the Moon's rotational ...
- 13.6k
4
votes
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Understanding gravity
The magnitude of the force of gravity between two bodies is proportional to the product of their masses:
$$F=G\frac{m_1m_2}{r^2}$$
This doesn't change depending on which body you're applying the force ...
- 33.7k
4
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Why can't gravity repel things?
Apart from the field-theoretical standpoint presented by Stan, one can repel objects in a sense, when taking orbital mechanics into account.
The slingshot maneuver extracts angular momentum and ...
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Intuition about why gravity is inversely proportional to exactly square of distance between objects
The validation is the same as the validation of any astronomical theory: it fits the data. Newton's law of gravitation was formed empirically, by observing the motion of the planets.
In particular, ...
- 273
4
votes
At what distance does MOND Modified Newtonian Dynamics take effect?
There is no line at which things transition from Newtonian dynamics to MOND, it's more of a gradual continuous transition depending on the nature of the interpolating function $\mu(x)$:
From Wikipedia ...
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votes
Gravitational attraction of Sun on distant object
James K gave a good answer to this, but I just want to add that if the Sun was unmoving relative to the center of the Milky-way, it would fall towards the center along with your object. The sun ...
- 22.9k
3
votes
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Precision of geocentric gravitational constant
Ignoring details such as the oblateness of the Earth, atmospheric drag, third body influences such as the Moon and the Sun, relativity, ..., the period of a satellite of negligible mass (even the ...
- 27.1k
3
votes
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Gravitation - Pulling or Pushing force?
In general relativity, gravity neither pushes nor pulls. To explain why ball travels in an arc you note the start and end points of the throw in 4d space time (3 space co-ordinates and 1 time ...
- 87.6k
3
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Gravitation - Pulling or Pushing force?
I'm guessing that this misunderstanding is a result of the oft-used rubber sheet analogy. The rubber sheet analogy says that, according to general relativity, mass curves space-time like a heavy ...
- 33.7k
3
votes
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How can I predict space directions?
If you project the orbits onto a plane, for example the plane of the ecliptic, the projections will cross. But that's only because you're looking at a 3D problem in 2D. If you look at the orbits in 3D,...
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3
votes
Why does a particle feel no force at radii greater than itself?
"in a spherically symmetric distribution of matter, a particle feels no force at all from the material at greater radii, and the material at smaller radii gives exactly the force which one would get ...
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Only top scored, non community-wiki answers of a minimum length are eligible