I've read in an answer to this question, of which I think that it was a very good, but somewhat long one, (I include the context in which it was written):

Let me expand this point. When this happens, not necessarily for a light wave but for whichever sort of wave, we say that the medium is non-dispersive. This is what your teacher meant with his "principle of wave constancy". It is a property of the medium and does not generally hold true, for elastic waves, for sound waves (a kind of elastic waves), etc. It may hold approximately - this happens for sound waves in air - or not hold at all: think of gravity waves we see at sea surface or on a lake, on a pond...

I'm a bit confused about what it's meant by that. Normally one would think that gravity waves are propagating distortions of space, though they are actually called gravitational waves. I can imagine that the pull of gravity causes the water waves, or is this exactly what is meant by calling these water waves gravity waves? Or is it that the waves are called gravity waves instead of gravitational waves so these waves have to be interpreted in a different way? But again, in what way? I have a gut feeling about what is meant but can't find the words for it.

I could have looked it up, I guess, but in this way also other users can benefit to improve their knowledge.

Who knows?


Gravity waves are a term of art used by people who study wave behavior in liquids or gases in which gravity and a free surface or a density difference are present. Gravity waves in the surface of water are the large, fast-moving ones stirred up by strong winds, that surfers ride on and that can crash over and capsize large ships at sea. In this special context, they have nothing to do with waves in the fabric of spacetime.

(The other type of surface waves in water are capillary waves, in which the restoring force that strives to smooth them out is not gravity but surface tension. These are tiny waves that move slowly, and are produced by things like wiggling insects floating on the surface of the water.)

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    $\begingroup$ It is presumably because of this prior art that the general relativistic phenomenon was named “gravitational waves”. $\endgroup$ – dmckee --- ex-moderator kitten Dec 16 '19 at 3:40
  • $\begingroup$ A very good-written answer and completely understandable! Thanks! (Though I ought to avoid writing this.) $\endgroup$ – descheleschilder Dec 16 '19 at 3:41
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    $\begingroup$ It's not just liquids that experience gravity waves. The atmosphere also experiences gravity waves that sometimes become visible in how they influence clouds. $\endgroup$ – David Hammen Dec 16 '19 at 9:41
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    $\begingroup$ One of the other other types of waves is a type of internal wave (but not the gravity type) that is more like trailing vortices, where their is no vertical displacement but there is motion at the surface.These show up in SAR images, usually offset from the source a bit because the surface motion gets mixed into the doppler processing. $\endgroup$ – JEB Dec 16 '19 at 16:58
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    $\begingroup$ Here's a link for atmospheric gravity waves: edition.cnn.com/2019/10/24/australia/… $\endgroup$ – molnarm Dec 18 '19 at 12:36

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