Talk:Orbital speed

2003

Heh, Anome, those edits worked out pretty well together considering we were both working pretty much blind to what the other was doing. :) -- John Owens

Oh, P.S. I'm not quite sure in my second equation, if that should be the mass of the other body, or the sum of their masses; I think it's really somewhere between the two, considering that radius for gravitational force will be from the other body, but radius of the orbit will be from the barycenter. I'll work this out soon. -- John Owens

Note on my latest equation, the one for two similar masses: I suspect it will work for elliptical orbits, if you treat either body as always being at the center of the ellipse for the purpose of calculating its semimajor axis, which you then use for r. -- John Owens

Electronic orbitals

In the atom, the speed of the orbital 1s is v=Zαc; how can I get the speed of the other orbitals?--Daniel bg 14:23, 28 December 2005 (UTC)[reply]

General relativity

I guess that under general relativity the stated speeds are not entirely correct, perhaps the article should include also the general relativistic counterparts to the classical speeds?Agge1000 15:28, 14 November 2007 (UTC)[reply]

Earth orbit section

There are some figures I couldn't understand where they come from:

|Molniya orbit||6,900 to 46,300 km||500 to 39,900 km||1.5 to 10.0 km/s||11 h 58 min||54.8 MJ/kg

Within a range of 500 to 39,900 km above the Earth, 1.5 to 10.0 km/s ? I've not yet checked all but only this due to the huge range of speed and the fact that 10 km/s is near from escape velocity from Earth surface.--Email4mobile (talk) 05:24, 11 July 2010 (UTC)[reply]

I've figured it out: some of these orbital speeds are calculated with respect to the tangential speed at the surface of the Earth (8km/s), and some are calculated with respect to a stationary frame. I'll have to fix this. SamuelRiv (talk) 17:07, 11 July 2010 (UTC)[reply]

With respect to the surface is quite different from with respect to a circular Earth orbit near the surface. Are you mixing up the two, with figures like "0.13 to 1.0 km/s circular, relative to surface" for LEO?--Patrick (talk) 00:08, 12 July 2010 (UTC)[reply]

Earth Surface Orbit

I don't know how the table got 0.5 km/s for a surface orbit, but the orbital velocity at 6400km is 7.89 km/s.

I have adjusted the table accordingly. — Preceding unsigned comment added by Trebudude (talk • contribs) 01:40, 5 June 2012 (UTC)[reply]

If you want to define surface orbit for equatorial radius, sqrt(3.986004415e14 / 6378137.0) = 7905.366 m/sec. DonPMitchell (talk) 18:35, 5 August 2013 (UTC)[reply]

The table displays the "orbital" speed of standing on the Earth's surface, which is not in fact an orbit at all. This is misleading. I have clarified the title of that line and added another row for a surface-level orbit using the numbers provided by DonPMitchell. Aubri (talk) 20:24, 30 June 2014 (UTC)[reply]

I would like to see more fantastic numbers for weird orbits, ie: shrink the mass of the earth to 1km diameter, at 4km circular orbit what speed is that? — Preceding unsigned comment added by 71.63.181.21 (talk) 07:17, 18 February 2018 (UTC)[reply]

This article is simply wrong.

This article has many factual errors, most either because of arbitrary and unstated assumptions or because of omission of critical qualifications. A paper last week (Oct. 2017) (sorry I don't have the citation) listed 600 families of orbits of 3-body systems (theoretically, modeled on a computer) which are far more complicated that simple ellipses. These orbits were (mostly) constrained to be in a plane (rather than in 3-d space) so form a subset of all potential closed orbits. Clearly these orbits will not have simple formulae for speed. A closed orbit is NOT an ellipse except in a simple two body (point-like) system. Satellites orbiting the Earth have velocities which vary due to the inhomogeneity of the Earths gravitational field (due to mass concentrations). This (obviously) means that the orbital speed is NOT a simple function of the larger object's mass, except as a (good) approximation. The assumption that an object can be treated as a center-of-mass point is an excellent approximation when periapsis is > 10 times the object's surface radius. Orbital speed needs to be better defined here, imho. If a satellite in a 'stable' orbit fires a bullet or rocket, then the position in the gravitational field changes little (at first) but the velocity may have changed drastically - it should distinguish between velocity and orbital velocity. General Relativity does not allow any real orbit to be stable. All so-called 'stable' orbits are only meta-stable. The orbits of the planets are predicted to be stable for the next 50,000,000 years, beyond that uncertainties in the various parameters (as well as the galactic background gravity field) allow for greater and greater potential deviation from the current orbital paths. In fact, there is some possibility that one of the inner planets will be ejected from the Solar System in the next 500 million years. In the section Mean Orbital Speed, while discussing TWO bodies, r is stated to be "the body's radius" with no regard for which body it is referring to. A rookie mistake. Finally, the lead conflates "the more massive body" with the system's barycenter. (Incidentally, the chaotic nature of orbital dynamics (over large times) is not related to the General Relativistic limitations on orbital stability - GR dissipation occurs (typically) over billions and trillions of years.)98.21.70.161 (talk) 18:06, 27 October 2017 (UTC)[reply]

Since no one has stepped forward to fix this awful article, I'm going to make a start.71.31.149.188 (talk) 13:46, 14 January 2018 (UTC)[reply]

I have attempted to edit the lead and the "Radial Trajectory" section to correct all of the blatantly misleading or ill informed things present. I understand I risk a compete undo edit here but there is just so much wrong about the article. First is the subtle point that most people understand speed as being an observational, measured, value; it is not model dependent. Defining it in terms of two-body systems or in terms of the falsified Kepler Laws is at best a crude approximation and at worst just plain wrong. I attempted to modify the sections after the Radial Section, but soon got in over my head. I frankly see no purpose in them. The terms introduced in them (i.e. traverse orbital speed) are DIFFERENT from and should, imho be kept separate from the term "orbital speed". I did not add anything which explains that while nearly everyone believes something in orbit is in a PERIODIC (repeating) circular (or elliptical) path that for some probably bad reason, open orbits are given nearly as much space here as closed orbits. I also did not remove all of the incorrect claims about the larger object being at the focus of an orbit. That's just rubbish.71.31.149.188 (talk) 15:46, 14 January 2018 (UTC)[reply]

FTR, the proposed edits were made, and were not nearly extreme as the above comments imply. For example, the new text notes that the barycenter can be assumed to be the center of mass of the larger body if the mass of the smaller is negligible, and putting the larger body at the focus is true under Keplerian assumptions, which only approximate the real world. I'm glad this editor noticed these assumptions and surfaced them while not discarding the simpler models which are still used in a lot of contexts. -- Beland (talk) 16:58, 24 July 2024 (UTC)[reply]

Speed or velocity?

If "Escape velocity" then "Orbital velocity" Voproshatel (talk) 10:44, 10 July 2020 (UTC)[reply]