Talk:Gravity wave

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Untitled[edit]

The page doesn't say what a gravitational wave is.

It does now -- I hope satisfactorily. — Toby 10:24 Nov 11, 2002 (UTC)

In case anybody does know: are gravitational waves supposed to be longitudinal waves or transverse waves? Ellywa 12:52, 24 Sep 2003 (UTC)

I got an answer from user:Andre Engels at nl:wikipedia, generally it is thought that these waves are transverse, based on general relativity. Ellywa 07:54, 25 Sep 2003 (UTC)

It has been proposed that they are a longitudinal scalar waves by some researchers (which my bet is on, though I'm probably wrong ... so everyone will have to wait for further data). It is really unknown [and may exhibit feature of both (i.e., Duality)]. JDR

Infragravity waves[edit]

Can someone help provide a definition for Infragravity waves? They are referenced in the article but it is confusing because they are never explained. —Preceding unsigned comment added by AmRadioHed (talk • contribs) 19:45, 19 March 2008 (UTC)[reply]

Gravitational waves do not change the strength of gravity.[edit]

The concept of "the strength of gravity will go up and down as a gravitational wave passes" is, at least for the case of small amplitudes, wrong.

A GW changes the distance between freely falling test particles, but it will not change the strength of gravity as such. Given a GW with sufficient amplitude passing by while you are standing on a bathroom scale, the reading on the scale would not change. Your legs might be shortened (or lengthened, depending on the phase of the wave), though.

gravity waves are waves generated from centifiqual force due to revolving around the sun,

Grammar and punctuation errors at the beginning of this article make it impossible to understand, even when the punctuation and subject/verb agreement is corrected:

In fluid dynamics, gravity waves are waves generated in a fluid medium (or at the interface between two mediums, e.g., the atmosphere or ocean) which has the restoring force of gravity or buoyancy.

"...which has the restoring force of gravity or buoyancy": Does that refer to the waves, or to the medium? ...and, in either case, what is meant by "the restoring force"?

The article should also explain why this phenomenon should be called a gravity wave when this term means something different when speaking of General Relativity. rowley 23:50, 28 December 2006 (UTC)[reply]

It clearly refers to the fluid medium, which is singular. If it was referring to the waves (plural) it would say "which HAVE". Also there is an article about "Gravitaional Waves", the term you are referring to in physics, and that article redirects you here along with explaining how gravitational waves are sometimes INCORRECTLY called gravity waves.70.125.103.247 01:26, 4 February 2007 (UTC)[reply]

Frankly I'm annoyed this page exists in it's current phrasing of 'gravity wave' rather than 'wave caused by gravity.' This wording causes too much confusion between it and 'gravitational waves.' —Preceding unsigned comment added by 98.144.5.92 (talk) 01:11, 5 April 2009 (UTC)[reply]

Weather[edit]

does a gravity wave in a cloud formation indicate anything regarding the intensity of an oncoming storm front or is it simply a phenomena in and of itself? I ask because i witnessed some clouds coming south off of Lake Superior in Upper Michigan (United States) and they preceded a very strong thunderstorm.

Undular Bore Waves[edit]

Should the article mention Undular bore Waves? This what I've always heard these called, even by NASA.

Edit: forgot to sign! Chaosratt (talk) 13:21, 13 May 2008 (UTC)[reply]

period question[edit]

The article says,

Gravity waves have a period of between 1 and 30 seconds (1 Hz to 0.033 Hz). Alternatively, infragravity waves generally have a period between 30 seconds to 5 minutes (0.05 to 0.005 Hz).

Are these ranges specifically for ocean waves on Earth, or is it a general physical property of gravity waves that their periods fall in that range? In general I find it hard in parts of this article to determine when it's discussing gravity waves as a general physics concept, and when it's specifically discussing that concept's most prominent application to the Earth's oceans. --Delirium (talk) 17:24, 6 October 2008 (UTC)[reply]

The whole terminology is quite confusing, and unfortunately this is also the case in many articles and textbooks on the subject. All mentioned bounds, if correct at all, are Earth conditions. Some comments:

Tsunami's are certainly gravity waves, as well as tides in the ocean (in shallow seas tides are also strongly affected by dissipation). Both have much larger periods. The indicated range seems to point at wind-generated gravity waves.
What is meant with period, since wind waves in a sea state are random?
For all gravity waves: the lower range limit of 1 second is definitely to high, since this limit is determined by surface tension (see capillary wave). Wave lengths above 0.1 ~ 0.2 m in case of a water-air interface are hardly influenced by surface tension and can be called gravity waves. This corresponds with periods above 0.3 second (taking 0.15 m as the wavelength).
The upper bound of the gravity waves seems reasonable for wind-generated waves, perhaps somewhat low. The wind can force the waves to greater height and longer wavelength as long as the phase speed of the waves is less than the wind speed. A 30 s wave corresponds with a phase speed of 45 m/s, which can be exceeded in extreme hurricanes and typhones, see Saffir-Simpson Hurricane Scale.
The term "infragravity wave" suggests somehow that these waves are affected less by gravity. The term is mainly used in coastal engineering to point at subharmonic waves due to non-linear interactions of the Fourier components in the wind waves. But these "infragravity waves" are just as subject to gravity as all other waves. Only in case they are bound/locked/coupled directly by non-linearity to components of the wind waves, these wave components move at a different speed as for gravity waves of the same frequency (but note they are in fact just a part of the gravity waves, only emerging by looking from a "Fourier transform" viewpoint at them). However, the term is also used for the gravity waves emanating in the same frequency band.
The given range of 30 s to 5 minutes for the "infragravity waves" seems arbitrary. Short wind-waves of 1 second may also be accompanied by subharmonics at, say 3 s.
The further statement in the text: "Infragravity waves can be felt rather than seen as they have a much greater wave energy." is pure nonsense, since the infragravity waves always have less energy than the wind waves they are non-linearly bound to. So I remove that.

The above comments are not NPOV (with respect to "infragravity waves") and not accompanied with references.

So I think you have a good point and there is quite some work to do here! -- Crowsnest (talk) 18:56, 6 October 2008 (UTC)[reply]

Ocean wave image.[edit]

The image of the ocean wave (see right) is lovely, and it matches what we normally think of as a wave; but if I'm understanding the article right, it seems like it's a bit misleading, because a "gravity wave" would be out in the middle of the ocean, oscillating periodically, rather than breaking on shore. (I mean, the breaking wave is still a wave, and not wrong per se, but just a bit misleading.) What do y'all think? Should we change to an image of non-breaking ocean waves?

—Ruakh_TALK 17:14, 15 April 2009 (UTC)[reply]

It is a form of a surface gravity wave, whether it is breaking or not, in the ocean or in a lake. Surface gravity wave is in fact the wide class of waves on a gas-liquid interface forced by gravity (and surface tension effects negligible). For me, this picture is fine and not misleading in itself. The caption could be better: "breaking surface gravity wave on an ocean beach" for instance. -- Crowsnest (talk) 17:36, 15 April 2009 (UTC)[reply]

Commons categories[edit]

Have I understood the distinction between Gravity wave and Gravitational wave correctly in my assigning of media to the Commons categories Commons:Category:Gravity waves and Commons:Category:Gravitational waves? Specifically, Gravity wave talks about hydrodynamic waves and fluids and I am unsure whether that also applies to the particle ripples seen in the rings of Saturn. I am also asking this at Talk:Gravitational wave#Commons categories. 84user (talk) 12:51, 1 May 2009 (UTC)[reply]

Gravity Waves in Space[edit]

I remember reading this was being studied by physicists. They were looking for (trying to prove or disprove) the existence of gravity waves traveling through space from distant events. Is this the same thing?

75.166.179.110 (talk) 20:16, 16 April 2010 (UTC)[reply]

No, those are described in: gravitational waves. -- Crowsnest (talk) 21:01, 16 April 2010 (UTC)[reply]

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Deep water waves; Hamiltonain formalism[edit]

There do not seem to be any existing articles on deep water waves? (currently a red-link). Airy wave theory is about linearized deep-water waves (but in general KdV is non-linear). Stokes wave is about periodic waves (but in general, waves are not periodic). Waves and shallow water is a stub.

From what I can tell, the foundational paper that provides a Hamiltonian formalism for deep water waves is this:

Zakharov, V. 1968 Stability of periodic waves of finite amplitude on a surface of a deep fluid. J. Appl. Mech. Tech. Phys. 2, 190–198.

The perturbation theory for this is first worked out here:

Krasitskii, V. P. 1994 On reduced equations in the hamiltonian theory of weakly nonlinear surface waves. J. Fluid Mech. 272, 1 – 20.

A nice review of the work is here:

Janssen, P. A. E. M. 2009 On some consequences of the canonical transformation in the hamiltonian theory of water waves. J. Fluid Mech. 637, 1–44.

I'm trying to slap together Draft:Resonant interaction and am trying to figure out what WP articles already exist on these topics. Apparently, the primary wave in which waves interact in deep water is a four-wave resonant interaction. There is a wicked-cool experimental paper on this here:

F. Bonnefoy, F. Haudin, G. Michel, B. Semin, T. Humbert, S. Aumaˆıtre, M. Berhanu, and E. Falcon, (2018) Observation of resonant interactions among surface gravity waves] J. Fluid Mech.

Any help with Draft:Resonant interaction appreciated. 67.198.37.16 (talk) 19:38, 15 September 2020 (UTC)[reply]

Unsourced, seemingly contradictory claims (frequency times period should be 2π).[edit]

I added a "citation needed" template to the contradictory claim that: "Wind-generated gravity waves on the free surface of the Earth's ponds, lakes, seas and oceans have a period of between 0.3 and 30 seconds (corresponding to frequencies between approximately 3 Hz and 33.3 mHz)". AFAIK, the product of the period and the frequency should be 2π so the numbers in that statement are inconsistent.

Presumably one of the two ranges is correct and the simplest fix would be to delete the other (unsourced) one. Regretfully I have not been able to find a reliable source that is not a circular references to this article so I can not determine which range is correct.

The phrase "wind generated" surface waves does seem to refer to a specific range of frequencies in the sense that frequencies outside that range are unlikely to be generated by wind. Annette Maon (talk) 11:21, 8 December 2022 (UTC)[reply]

It looks OK to me. See Frequency. Dondervogel 2 (talk) 11:41, 8 December 2022 (UTC)[reply]

Yes, it is fine. The frequency of a phenomenon times its period is 1. Angular frequency times period is 2π. —Quondum 13:41, 8 December 2022 (UTC)[reply]