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From: Matthew Lybanon on 11 Dec 2009 11:10
In article <7e0c6$4b21837b$5039815f$4346(a)news.chello.nl>,
Bert Harleman <bert(a)bytegraag.nl> wrote:

> Suppose you measure the speed of waves at open sea (with a large depth)
> Then suppose you change the ocean water with a liquid that has twice the
> mass.
> Will the waves travel faster? Or slower?
>
> I found the next part of information:
> > Wave speed is also dependent on the density of the
> > medium. The denser the medium (for the same phase of a medium,
> > in this case a liquid), the slower the speed of a wave
> > of a particular frequency. Since sea water can vary in density
> > (density is determined by temperature, depth, and salinity),
> > waves in the ocean can vary in wave speed depending on the sea
> > water density.
>
> Waves are formed by the wind. Moving denser liquid requires more energy,
> so I think these waves are less high. But what would the effect on the
> speed be?

In deep water, the phase speed of long surface gravity waves is
essentially independent of the density. The group speed is about half
the phase speed, also independent of density. On the other hand, for
surface capillary waves (for which the restoring force is surface
tension rather than gravity) the phase speed decreases with increasing
density. So, for a mixture of the two types of waves--which is what you
get in the real world--there is a density effect.

The reference has more details: dispersion characteristics, amplitudes,
etc.

Ref.: J. R. Apel, Principles of Ocean Physics, Academic Press, 1987
(chapter 5). Other books on fluid dynamics or physical oceanography
should cover the same material.
From: Bert Harleman on 11 Dec 2009 17:22

> Moving denser liquid does require more energy. With a denser liquid,
> gravity provides more energy. Falling objects give a clue as to what we
> might expect from gravity waves (i.e., waves in a liquid driven by
> gravity): independence of wave speed on density.
>
> If something other than gravity provides the force (e.g., surface tension
> waves a.k.a. capillary waves), then density will matter very much.

If the ocean contains big waves (amplitude) they must be gravity waves,
most probably formed by the wind?

Is it right that additional capillary waves then have very little effect
on wavespeed (when density of the liquid is changed)?


> Some useful detail on
> http://en.wikipedia.org/wiki/Dispersion_(water_waves)

From: Androcles on 11 Dec 2009 17:53

"Bert Harleman" <bert(a)bytegraag.nl> wrote in message
news:19e8c$4b22c634$5039815f$12156(a)news.chello.nl...
>
>> Moving denser liquid does require more energy. With a denser liquid,
>> gravity provides more energy. Falling objects give a clue as to what we
>> might expect from gravity waves (i.e., waves in a liquid driven by
>> gravity): independence of wave speed on density.
>>
>> If something other than gravity provides the force (e.g., surface tension
>> waves a.k.a. capillary waves), then density will matter very much.
>
> If the ocean contains big waves (amplitude) they must be gravity waves,
> most probably formed by the wind?

http://paws.kettering.edu/~drussell/Demos/waves-intro/waves-intro.html





> Is it right that additional capillary waves then have very little effect
> on wavespeed (when density of the liquid is changed)?
>
>
>> Some useful detail on
>> http://en.wikipedia.org/wiki/Dispersion_(water_waves)
>


From: Bert Harleman on 11 Dec 2009 18:17

> http://paws.kettering.edu/~drussell/Demos/waves-intro/waves-intro.html

Thanks, you must be thinking I'm an idiot.
I get a good idea of different waves types, how they transfer energy.

What still puzzles me is if large (gravity) oceanwaves and capilary
waves interact in a way that changes the velocity of the gravity waves.
From: Androcles on 11 Dec 2009 18:55

"Bert Harleman" <bert(a)bytegraag.nl> wrote in message
news:2dd27$4b22d329$5039815f$25604(a)news.chello.nl...
>
>> http://paws.kettering.edu/~drussell/Demos/waves-intro/waves-intro.html
>
> Thanks, you must be thinking I'm an idiot.
> I get a good idea of different waves types, how they transfer energy.
>
> What still puzzles me is if large (gravity) oceanwaves and capilary waves
> interact in a way that changes the velocity of the gravity waves.

A capillary wave is a wave traveling along the phase boundary of a fluid,
whose dynamics are dominated by the effects of surface tension.

What do you imagine would happen if you used a hot soap bubble
(which relies on surface tension) to hold up this basket?
http://www.fantasyfliers.com/balloon001.jpg
That's the same effect surface tension would have on a tsunami.
I must be thinking you have no concept of scale.




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