43 votes

What is the shape of orbit assuming gravity does not depend on distance?

Circular orbits are always possible for any central force law, but noncircular orbits would resemble rosettes. Here's a specific example for the case where the force is constant with distance: By ...
Sten's user avatar
  • 4,511
16 votes

Does the escape velocity formula take into account how a gravitationally bound object's distance to its primary increases before coming back down?

The escape speed is defined in Newtonian physics simply by demanding that the sum of kinetic energy at launch (ballistically, with no power applied thereafter) and gravitational potential energy at ...
ProfRob's user avatar
  • 149k
12 votes

Does the escape velocity formula take into account how a gravitationally bound object's distance to its primary increases before coming back down?

Yes, escape speed is an instantaneous calculation at the distance 'r' from the center of the object, as that changes you have to recalculate your escape speed. For example, these are the escape ...
Jason Goemaat's user avatar
8 votes

What is the shape of orbit assuming gravity does not depend on distance?

In addition to Sten's great answer, it should be noted that under constant gravity all orbits are bounded. Therefore, there aren't any orbit like the hyperbolic ones mentioned in the question. That ...
Pere's user avatar
  • 1,750
7 votes

Does MOND change general relativity?

To incorporate MOND changes do need to be made to the theory of relativity. This is because at small accelerations and speeds, the theory of relativity approximates to normal Newtonian mechanics. ...
James K's user avatar
  • 119k
7 votes
Accepted

Are there really confined Globular Clusters?

You are asking for a star cluster that sits at the bottom of an infinite potential well. Such clusters do not exist because they are largely the source of the potential that they reside in. There are ...
ProfRob's user avatar
  • 149k
5 votes

Gravitational waves vs. "normal gravity"

Acceleration isn't a property of spacetime per se. Two test particles at the same location can have different instantaneous accelerations, so just knowing that there is a passing gravitational wave ...
benrg's user avatar
  • 3,822
4 votes

Gravitational waves vs. "normal gravity"

A gravimeter gauges the Earth's gravitational force by measuring the resistance it imposes on free fall. Technically, it is not measuring acceleration due to gravity, it measures the upward force ...
eshaya's user avatar
  • 3,641
4 votes

What is the shape of orbit assuming gravity does not depend on distance?

There wouldn't be standard orbits at all. The Earth orbits the Sun because the Sun's mass dominates the local spacetime. By removing distance from the gravitational equation, the Earth would, with ...
Michael Richardson's user avatar
3 votes

Are there really confined Globular Clusters?

Disregarding the example of globular clusters (which are all undergoing evaporation, as ProfRob points out), there are a couple other candidates for "isolated" astrophysical systems. The ...
Tom Donlon's user avatar
3 votes

Does the escape velocity formula take into account how a gravitationally bound object's distance to its primary increases before coming back down?

The escape velocity is based on how much energy it takes to go "infinitely" far away from the object. That is, the escape velocity is a velocity such that for any $r$, the amount of work ...
Acccumulation's user avatar
3 votes

Gravitational waves vs. "normal gravity"

In principle yes, in practice, probably not with current technology. If a gravitational wave passes through the Earth then the Earth will respond by expanding and contracting. As a result, there will ...
ProfRob's user avatar
  • 149k
2 votes

Gravitational waves vs. "normal gravity"

This depends entirely on the signal-to-noise ratio (SNR > 10?). The safest way is to try it out, because a repeatable experimental result is better than any philosophical discussion. The stress $h_{...
9herbert9's user avatar
2 votes

Does the escape velocity formula take into account how a gravitationally bound object's distance to its primary increases before coming back down?

Yes, it does. A good way of looking at this is to take not the difference in the object's velocity and the escape velocity at a given height, but at the difference between the object's velocity ...
Martin Kochanski's user avatar
1 vote

Are there really confined Globular Clusters?

Well, things like small asteroids are self-gravitating and confined to a pretty well defined volume. We believe they are approximately in thermal equilibrium. But it isn't gravity that brings them to ...
John Doty's user avatar
  • 1,726
1 vote

Does MOND change general relativity?

No, because General Relativity is well-tested (especially on solar system scales) and there is no indication it is incorrect in any way. If anything, it is MOND that needs to be tuned such that it ...
Allure's user avatar
  • 4,245
1 vote

How can Deep MOND regime apply inside a star?

Hi bit late to the party but I think there are two issues here. 1) How to deal with superpositions of small Newtonian gravitational accelerations and their conversion to the Milgromian expectation and ...
Mark Huisjes's user avatar
1 vote

Can I measure the moon's gravity?

The Shortt Free Pendulum clock was able to detect the variation in gravity due to the moon and also detected the nutations of the earth's precession. Shortt's clock was tested at the US Naval ...
rgarnett's user avatar

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