# Thread: Ripple effect in a fluid.

1. Situation 1: In a controlled environment a ball is dropped in the center a large tank containing water.
Situation 2: Same conditions as above only the second ball is the same size only it has more mass.
Question: Will the ripples in situation 1 reach the edge in the same time frame as situation 2?

2.

3. Originally Posted by spinner42
Situation 1: In a controlled environment a ball is dropped in the center a large tank containing water.
Situation 2: Same conditions as above only the second ball is the same size only it has more mass.
Question: Will the ripples in situation 1 reach the edge in the same time frame as situation 2?
Yes. If you want a broader explanation just ask

4. Thanks.
Would the wavelength be the same in both cases?

5. No the weight of the heavier ball would displace the water greater due to the more energy behind the collision. The waves would be higher and as a result the length of the water would contract and you'd therefore have a wave that would be more longitudinal than transverse.

6. Originally Posted by svwillmer
No the weight of the heavier ball would displace the water greater due to the more energy behind the collision. The waves would be higher and as a result the length of the water would contract and you'd therefore have a wave that would be more longitudinal than transverse.
I'd suspect that amplitude has little to do with frequency. As you correctly point out, ceteris paribus the waves on the surface of water will travel at the same speed. If created by an object with the same frequency, then the wavelengths will be the same, even if their amplitudes differ.

Assuming Galileo's famous thought experiment, Leaning Tower and so on, still holds, the two balls should reach the surface of the water at the same velocity, ergo, produce waves of the same frequency. The second, heavier, ball should impart more energy to the water which should, I suppose, increase the amplitude of the waves, but this should be independent of the other issues (wavelength, wave velocity etc).

cheer

shanks

7. So, just to ask: If the two balls were of the same mass, but hit with different velocities (perhaps dropped from different heights), would the ripples move faster toward the edge, or just have a higher frequency?

8. Originally Posted by kojax
So, just to ask: If the two balls were of the same mass, but hit with different velocities (perhaps dropped from different heights), would the ripples move faster toward the edge, or just have a higher frequency?
Neither. Again, as above, the amplitude would be different. Frequency, of course, is a function of multiple wave-crests. A single wave-crest, a single moving ripple, could not really be considered to have a wavelength or frequency at all - it isn't cyclical if it had a crest and a trough you might - but I'm not going there).

To that extent, all talk of frequency is moot in a single impact/ripple scenario (and I'm not knowledgeable enough to talk about the complex multiple wave forms created by a single splash), and so the only variables in such an experiment would be amplitude (how much energy went into the splash) and velocity (the conditions of the water that determine the speed of a surface wave). Please not that the second variable - speed - is independent of the nature of the body causing the wave/ripple.

cheer

shanks

9. Originally Posted by sunshinewarrio
Please not that the second variable - speed - is independent of the nature of the body causing the wave/ripple.

cheer

shanks
Shanks, how does that jibe with the reported information that the recent Asian tsunami wave traveled at 500km/h or faster? Ripples caused by a stone dropped in a pond don't travel that fast. I haven't thought it through, but it seems to contradict what you are saying. I dunno. Just wondering.

Bunbury

10. Think of it this way. If a wave has a high frequency, or a low frequency they may both have more energy, but will still travel at the same speed. Just like light agianst gamma rays or radio waves. However, if there is a big splash in water, from a massive object, the water displaced will make the water receed to the point due to the energy behind impact (which is why tsunamis cause shore waters to receed where a stone being dropped in miles away would not do so. But the waves would travel at the same speed, unless something sped them up).

11. Originally Posted by svwillmer
(which is why tsunamis cause shore waters to receed where a stone being dropped in miles away would not do so. But the waves would travel at the same speed, unless something sped them up).
tsunamis travel at hundreds of miles an hour and have very long wavelengths.

12. Originally Posted by Bunbury
Originally Posted by sunshinewarrio
Please not that the second variable - speed - is independent of the nature of the body causing the wave/ripple.

cheer

shanks
Shanks, how does that jibe with the reported information that the recent Asian tsunami wave traveled at 500km/h or faster? Ripples caused by a stone dropped in a pond don't travel that fast. I haven't thought it through, but it seems to contradict what you are saying. I dunno. Just wondering.

Bunbury
I suspect there is a difference in the way waves travel in water, depending upon circumstances. Way too complicated for me to think about (given my lack of technical background) or, therefore elucidate, but here are some speculations.

1. There are at least two types of waves in water - transverse and longitudinal.

2. Simple transverse waves will have their speed affected by certain characteristics of water, including density and surface tension (when they are small enough, as it were), plus, since they are transverse waves on the surface, gravity.

3. Longitudinal waves, most usually implicated in carrying sound through water, customerily travel at immense speeds, up to and including 500kmph.

4. I presume that the tsunami was a more complicated waveform than the simple small surface ripples I was speaking of, and may have had characteristics of a shock wave (a single blast of sound!), and that may help account for it.

Of course, these are quite wild, and ill-informed speculations on my part, but I'd be happy for any fluids mechanic/engineer or oceanographer to correct me.

Thanks for the question - always good when something makes you think, eh?

cheer

shanks

13. Is googling a suitable alternative to thinking? If so I've come up with this:

A wave is characterized as a shallow-water wave when the ratio between the water depth and its wavelength gets very small. The speed of a shallow-water wave is equal to the square root of the product of the acceleration of gravity (32ft/sec/sec or 980cm/sec/sec) and the depth of the water. The rate at which a wave loses its energy is inversely related to its wavelength. Since a tsunami has a very large wave length, it will lose little energy as it propagates. Hence in very deep water, a tsunami will travel at high speeds and travel great transoceanic distances with limited energy loss. For example, when the ocean is 20,000 feet (6100 m) deep, unnoticed tsunami travel about 550 miles per hour (890 km/hr), the speed of a jet airplane.
http://wcatwc.arh.noaa.gov/physics.htm

Conversely, a pond ripple would be a deep water wave, since its wavelength might be a copile of inches in a pond several feet deep so would not behave according to the formula mentioned.

14. Originally Posted by Bunbury
Conversely, a pond ripple would be a deep water wave, since its wavelength might be a copile of inches in a pond several feet deep so would not behave according to the formula mentioned.
Yes. Yes. Zigackly. Didn't I say so? Ha ha.

Thanks for that.

Now all I have to do is get my head arouns solidon (soliton?) waves that appear to have almost a super-conducting effect (no loss of energy)... :-D

15. Didn't I say so?
Sort of...
:P

16. Not to deviate from the original questions the tsunami would not apply as the tank in question would have no shoal and the wave height would remain the same from origin to impact of the tank side. So it appears that the wave velocity of situation 1 is the same as situation 2. Right?

17. Originally Posted by spinner42
Not to deviate from the original questions the tsunami would not apply as the tank in question would have no shoal and the wave height would remain the same from origin to impact of the tank side. So it appears that the wave velocity of situation 1 is the same as situation 2. Right?
Right.

18. Originally Posted by spinner42
Not to deviate from the original questions the tsunami would not apply as the tank in question would have no shoal and the wave height would remain the same from origin to impact of the tank side. So it appears that the wave velocity of situation 1 is the same as situation 2. Right?
YES! I keep saying that.

19. I tend to think that all tings in our universe, as we know it, have a relationship. Therefore I put forth that given the water experiment and the photon then the energy of all mater is the same for a given wavelength. Right?

20. Originally Posted by spinner42
I tend to think that all tings in our universe, as we know it, have a relationship. Therefore I put forth that given the water experiment and the photon then the energy of all mater is the same for a given wavelength. Right?
Time, more energy is given over more time. Hence a wave has more energy if it oscillates FASTER. Which results in a greater frequency.

21. So frequency and energy have a one to one correspondence. Right?

22. Originally Posted by spinner42
So frequency and energy have a one to one correspondence. Right?
E = hf

Here E = energy of a photon
h = Plancks constant, which is 6.626x10^-34 J.s, (Joules per second (I think the s means second)
f = the frequency of the photon

If the energy was less and you moved it around in the forumla then you'd see that if the Planck constant remained constant then obviously frequency is the one that must change. So yes they have a one to one correspondance, like mass and energy equivalence. Everything in the universe can be measured with one equation-we've just yet to find that equation.

PS My last post here above was my 666th. The number of the beast.

23. However with the photon the energy transfer is E=hc/wavelength (lambda). Therefore the E is a function of lambda where “h” and “c” are constants. So, would this equation hold true for the water example where one could back calculate the energy based on lambda?

With luck the number of the beast will have passed without negative effect.

24. Originally Posted by sunshinewarrio
Originally Posted by spinner42
Not to deviate from the original questions the tsunami would not apply as the tank in question would have no shoal and the wave height would remain the same from origin to impact of the tank side. So it appears that the wave velocity of situation 1 is the same as situation 2. Right?
Right.
I haven't read anything here to justify that assertion. :P

25. Originally Posted by Bunbury
Originally Posted by sunshinewarrio
Originally Posted by spinner42
Not to deviate from the original questions the tsunami would not apply as the tank in question would have no shoal and the wave height would remain the same from origin to impact of the tank side. So it appears that the wave velocity of situation 1 is the same as situation 2. Right?
Right.
I haven't read anything here to justify that assertion. :P

Oooooh you horror. What's your theory then?

26. Originally Posted by sunshinewarrio
Oooooh you horror.
Thank you. Thank you very much.

What's your theory then?
My theory, which I shall attibute to Professor Google, is that very small ripples are called capillary waves, and they have a property called group velocity, which is the average speed of the group, which can contain individual ripples traveling at different speeds, but none can break out of the group. The fastest get pulled back and the slowest peter out. (A sociological metaphor in there somewhere.)

The minimum group velocity in water is 23 cm/s. The group velocity is dependent on wavelength, and wavelength is dependent on excitation energy, thus the group speed is a function of the mass of the object dropped.

That's about as far as Prof. Google could go. He said if you really want to understand this complicated phenomenon you need to read a book, but since the consensus here seems to be that if it ain't on the internet it ain't worth the paper it isn't written on, we'll have to continue languishing happily in ignorance.

27. Originally Posted by Bunbury
Originally Posted by sunshinewarrio
Oooooh you horror.
Thank you. Thank you very much.

What's your theory then?
My theory, which I shall attibute to Professor Google, is that very small ripples are called capillary waves, and they have a property called group velocity, which is the average speed of the group, which can contain individual ripples traveling at different speeds, but none can break out of the group. The fastest get pulled back and the slowest peter out. (A sociological metaphor in there somewhere.)

The minimum group velocity in water is 23 cm/s. The group velocity is dependent on wavelength, and wavelength is dependent on excitation energy, thus the group speed is a function of the mass of the object dropped.

That's about as far as Prof. Google could go. He said if you really want to understand this complicated phenomenon you need to read a book, but since the consensus here seems to be that if it ain't on the internet it ain't worth the paper it isn't written on, we'll have to continue languishing happily in ignorance.
Interesting. Thanks for that. By that notion, therefore, are we suggesting that the energy of the impact (with which this thread began) could affect the velocity of the ripple it causes?

28. Yes, that’s how I interpret some things I’ve read, although nothing is that explicit. I also saw mentioned that the phenomenon of laser light exceeding C is explained by this group velocity idea, in that the overall velocity for the group cannot exceed C, while some components perhaps can (garbled no doubt, but something vaguely like that).

29. The first reply to the original question stated under both situations the waves would reach the edge at the same time. What was stated last seems to imply just the opposite.

30. This is a crosslink to another forum where this subject is discussed but an explicit answer to your question isn't given. Two books, Lamb and Segel, are suggested as places to look. The Google page on capillary waves gives some information, but again no explicit answer. After reading through some of this stuff I concluded that the answer to the original question "Will the ripples in situation 1 reach the edge in the same time frame as situation 2?" is no, but I'm certainly not sure.

http://physicsforums.com/archive/ind.../t-177519.html

 Bookmarks
##### Bookmarks
 Posting Permissions
 You may not post new threads You may not post replies You may not post attachments You may not edit your posts   BB code is On Smilies are On [IMG] code is On [VIDEO] code is On HTML code is Off Trackbacks are Off Pingbacks are Off Refbacks are On Terms of Use Agreement