Speed of waves

[blinky8225]

My one science teacher says that when a wave goes through a uniform medium the speed will remain the same when you apply energy and my other says that the speed should change if you apply more energy. Can you please tell me which is right? Can you also provide proof?

 

[TK]

Good luck blinky. Wish I could find a good book on the subject, but I think you and I might be dead on this for now.

TK

 

[jagec]

what kind of wave are we talking about? What kind of "power" are you applying? More info is needed.

 

[MetalStorm]

Electro Magnetic waves travel at the speed of light, so increasing their energy or in this case frequency will have no effect on their speed as they are already traveling as fast as they can go.

 

[itachi]

if that's what your second teacher said.. and he was referring to a travelling wave, then he's wrong. just to be anal.. energy can't be applied to a system. work is done on a system, power applied.

to answer your question.. if the material that the wave is travelling through is uniform, then it is literally impossible for the speed of the travelling wave to change. i can't give you a real proof since i don't know much about the wave equation.. but simply put, if what your teacher said was true.. that power applied to a travelling wave increases its velocity in a uniform material, then the speed of sound and light wouldn't be constant in air, water, etc..

if your teacher was referring to a standing wave, then work done on the x-axis would increase the velocity.

 

[silverpig]

More energy in wave = higher amplitude (or frequency, or both...)

 

[CycloWizard]

nm

 

[drklrd23]

One thing to keep in mind is that waves are quite a bit different from the standard mechanical physics which you're probably used to. There are two ways to increase the energy in the system - increase the amplitude of the waves or increase the frequency of the wave (since power is defined as energy per unit time). In general, since the wave velocity is dependent on wavelength and frequency, then increasing the frequency will increase the velocity.

Summary:
Both professors are technically right. If the amplitude of the wave is increased, then the velocity will not change; if the frequency is increased, then the velocity will increase.

 

[itachi]

Originally posted by: drklrd23
One thing to keep in mind is that waves are quite a bit different from the standard mechanical physics which you're probably used to. There are two ways to increase the energy in the system - increase the amplitude of the waves or increase the frequency of the wave (since power is defined as energy per unit time). In general, since the wave velocity is dependent on wavelength and frequency, then increasing the frequency will increase the velocity.

increasing the frequency will not increase the velocity. the velocity of a travelling wave is constant. if the frequency increases, wavelength decreases. v = 2 * pi * freq * lambda.

like i said before.. if it were physically possible for the speed of propagation of a travelling wave to increase in a uniform material then the speed of sound wouldn't be a constant.

 

[Googer]

Maybe one of your teachers was refering to sizemic or soud waves, they travel at differant speeds depending on what material they are passing through.

 

[Addis]

Wave speed = frequency(Hz) * wavelength(m)

So its impossible to change the speed because as you increase the wavelength the frequency falls etc

 

[TK]

So, if a submarine is in deep ocean and someone inside hits the hull with a wrench, a sound "wave" will be generated that travels from that point at something more than 4800 fps. If that someone then sets off a stick of dynamite that tears apart the hull, a big sound will be generated that will travel at the same speed as the wrench rap. Is there something other than sound that moves away from that point that can travel hundreds of miles (and what form could that take)? If one of the nuclear warheads in that submarine detonates, lots of new things will happen, but surely one would be a really big sound, which moves at the same speed as the other events. Is there another "effect" that will travel, tsunami like, away from that point, and what might be the physics of that "effect?

Again, any good books on the subject?

TK

 

[imported_mitch2891]

It does sound like the two professors were referring to different kinds of wave, like the experiment they often do early in physics where two people hold a rope one at each end and one shakes there end back and forth to create waves up and down the rope and in a case like this with non - electro magnetic waves the speed can indeed change.

Electro magnetic waves always have the same speed regardless of the wavelength or frequency. If you change either the other one changes to compensate so if you do increase the frequency then wavelength will shorthen resulting in more complete wave forms passing a given point in a given time frame but the speed of each wave will still be the same. A good way to show this is visible light as all the colours have a different wave length but for example does green travel faster than red? Nope they are all the same.

 

[MetalStorm]

Originally posted by: TK
So, if a submarine is in deep ocean and someone inside hits the hull with a wrench, a sound "wave" will be generated that travels from that point at something more than 4800 fps. If that someone then sets off a stick of dynamite that tears apart the hull, a big sound will be generated that will travel at the same speed as the wrench rap. Is there something other than sound that moves away from that point that can travel hundreds of miles (and what form could that take)? If one of the nuclear warheads in that submarine detonates, lots of new things will happen, but surely one would be a really big sound, which moves at the same speed as the other events. Is there another "effect" that will travel, tsunami like, away from that point, and what might be the physics of that "effect?

If I understand your question correctly, the difference between being able to hear the dynamite much further away from the point of detonation as apposed to the wrench is simply because the waves that were generated by the explosion probably have orders of magnitude more energy than those made by the wrench, that's why you'd be able to hear the dynamite explosion from much further away.
As far as I know there are no other things involved unless you were to set off a nuclear device which would generate gamma radiation, however they would only travel a short distance.

 

[TK]

itachi,

If the speed of propagation of a travelling wave thru a medium is the speed of sound thru that medium, then, what KIND of wave (composition of the wave) is the tsunami that it travels at not only less than the speed of sound, but might travel at a different speed than another tsunami (or "wave" generated by a different mechanical event)?

TK

 

[TK]

MetalStorm,

You did misunderstand my question (or I once again didn't make it very clear - I do that a lot). What I keep trying to ask is: What is different that two separate events, one relatively small - one relatively large both cause sound to travel at the same speed, but the large one, at least, also can cause another kind of "wave" (tsunami, shock, whatever) that moves at not only a slower speed than sound, but might travel at different speeds if some event parameter changes (magnitude, velosity, whatever)?

TK

 

[MetalStorm]

Oh, sorry about that!

As with Tsunami waves and waves on the sea in general, they are a mixture of transverse and longitudinal motion but out of phase by about 90 degrees - this results in an almost circular motion, I'm sure there's probably something on "how stuff works" about it, I'll have a look in a minute.
As to why the Tsunami wave travels so much faster than standard sea waves, I would guess that is due to the magnitude of the wave.

 

[itachi]

Originally posted by: TK
itachi,

If the speed of propagation of a travelling wave thru a medium is the speed of sound thru that medium, then, what KIND of wave (composition of the wave) is the tsunami that it travels at not only less than the speed of sound, but might travel at a different speed than another tsunami (or "wave" generated by a different mechanical event)?

TK

so i assume that you can prove it possible for 2 completely unrelated tsunami causing waves to travel? the speed of the wave that causes a tsunami can be seen as the speed that the water molecules themselve travel.. the speed that you're referring to, the speed that the peak travels at, is associated with the frequency of the wave.

edit: whoops.. meant to say "2 completely unrelated tsunami causing waves to travel at different speeds".

 

[TK]

itachi'

I can't prove any of the things I am asking about - that's why I am asking. I believe the speed of a sound is "known" and accepted by most, but I have heard different speeds referred to about other "waves?", and that is what I would like some proof of.

TK

 

[itachi]

oh.. thought u were asking a rhetorical question.

what other waves? can't give you any proof if i don't know what you're talking about..

 

[TK]

I surrender ya'll.

Thanks for all the responces anyway.

TK