What is the cutoff speed-of-sound for humans to distinguish direction in water?

[misskitty]

Why does the frequency change, using your example of the tongs, depending upon when you hit the tongs? I don't mean different surfaces you strike them on, you can include that should you like too, but if you strike them on a table at the end of the tongs and then again, but closer to where you are holding them.

I'm not sure if what I'm asking makes sense...

 

[whozum]

Hit your hand against a table. Doesn't make a very nice ring does it. The frequency is pretty low and the wave is so dampened that the sound kind of sucks. Tongs on the other hand are metal and usually have long 'fingers'. The longer the finger, the higher the frequency. I'm not really sure how to describe how this happens, but there's a lot more energy released when you hit a farther point. Higher energy waves have are frequency waves, since energy is proportional to frequency.

 

[misskitty]

Ah, no it does make sense. So is it safe to say the higher the frequency the more energy is carried on the wave? I was pondering what reasoning I used on my recent physics test.

 

[Ouabache]

So wait, if they weren't looking for the backround radiation waves, what were they looking for? Did they contact Dicke and Peebles and let them know what they found?

They were working for AT&T and experimenting with microwaves, presumably to learn more about them and to use them for telephone communications, say point-to-point on land or to transmit and receive microwaves via satellites.

That seems little acinine, why didn't they get mentioned? One would have thought they would have at least gotten a mention.

Well they are certainly mentioned today in historical perspective of how this discovery unfolded. However the Nobel Prize committee didn't include them in their award. We would have to do a little more digging to find out if they were mentioned when Wilson and Penzias published their findings.
If you're interested in learning more on this story, there is a good read at ---> http://www.princeton.edu/~paw/archive_new/PAW00-01/03-1025/features2.html
See part that begins "Thirty-five years ago, the Princeton Gravity Group, including professors Robert Dicke, Jim Peebles and David Wilkinson, were already building an experiment to detect the distant CMB (cosmic microwave background)..."

They have some wicked good shows.

That's for sure! I've watched the Stephen Hawking Universe several times (i have his book by same name). It never ceases to amaze me what this fellow comes out with, under such adversity.. Brian Greene's The Elegant Universe is another favorite. An astrophysics classic (i sent away for this one), Carl Sagan's COSMOS .. I've found quite a few more good science videos at the public library. The NOVA series is excellent as is Alan Alda's Scientific American Frontiers

 

[Ouabache]

Here's a question I just thought of. We were discussing resonance in my physics class today. We defined it, but I don't think the definition was very comprehendable. Honestly it was rather confusing.

Anyway, I know it has to do with something wanting to vibrate at a certain fundamental frequency. I know mechanical waves are affected by resonance because sound resonates. Does resonance occur with EM waves too? If so, what happens?

Sometimes it is hard to form a clear concept, from a definition. Examples are always much better.

When you swing on a swing in a playground, did you ever wonder why it swings at a certain rate? As you bend your knees and swing higher, you increase the amplitude of this system but you do not change the velocity. The swing and you move at a natural frequency. The system is resonant. If you try to swing faster or slower, you find that you cannot. That is how a pendulum works.

see ---> http://hyperphysics.phy-astr.gsu.edu/hbase/sound/reson.html#c2

If you are familiar with musical instruments, a clarinet is a good example for resonance of acoustic waves. Each key that is held down creates a cylindrical cavity (of a specific length) that is open at one end and blocked at the other. As you try to play a low note a lot of sqawking sound will occur until you find a certain note that will resonate for that length of pipe. Other pitches will also resonate for the same length of pipe and sound higher, those are harmonic frequencies and are related to the lowest (fundamental) note. A church pipe organ is certainly another good example of resonance.

see ---> http://www.umanitoba.ca/faculties/arts/linguistics/russell/138/sec4/resonanc.htm

Electromagnetic waves also exhibit resonance. In a radio, you can tune the dial to a certain frequency, to hear your favorite station. However the reception may be poor. You can improve the reception by making an antenna with the correct geometry (length of its elements), such that it resonates at the same frequency as the radio waves traveling through air. If you made the antenna a bit longer or shorter, the antenna would no longer resonate at that frequency and reception would get weaker. (there is a bit more to antennas than that, but this illustrates the point)

If you're curious about antennas a good read can be found at --->
http://www.qsl.net/g3yrc/antenna basics.htm
they have a nice diagram of the electromagnetic spectrum from power line frequencies all the way up to cosmic radiation.

Lots of shapes resonate, including bridges. A famous instance was the "Tacoma Narrows" suspension bridge in Washington state. It was noticed that as the winds blew, this bridge would begin to swing. When the wind reached 42mph, the bridge began to oscillate at its resonant frequency, creating both transverse (side to side) and longitudinal (length wise) oscillations. Eventually the amplitude became so great that the entire suspension collapsed.

For some vivid photos, see ---> http://www.lib.washington.edu/specialcoll/tnb/

 

[Reshma]

Hi Misskitty, good to have you back.

Acoustic waves like the ones from a guitar or in an auditorium or any other kind of instrument? Ocean waves, that would be like the tsunami. The seismic waves, aren't they measured using logarithmic functions? I don't know much about them, just that they are measured on a seismegraph. Matter acts as interferrance right?

The term "Acoustics" is the branch of physics which studies sound, mechanical waves in gases, liquids, and solids. So any kind of study of sound waves be it music, seismology etc. falls under acoustics. For more check out this link: http://en.wikipedia.org/wiki/Acoustics.

Seismic waves are waves that travel through the earth(waves can be due to any natural phenomenon viz. earthquake, volcanoes etc.) A seismograph is basically a device which can detect and measure the intensity of seismic waves. If you are interested in learning how a seismograph works check out this link: http://en.wikipedia.org/wiki/Seismograph

Related question to sound; why do things echo in caves and rooms that have nothing in them? Doesn't sound have an easier time traveling through a solid medium because the molcules vibrate easier and they make the neighboring molecules vibrate quickly too?

Echoes are a diferent phenomenon altogether.
An "echo" occurs when sound reflects back to the listener from rocks or other hard surfaces, especially flat vertical surfaces. The human ear cannot differentiate between two sounds if they occur together within a time interval of 1/17th of a second(the exact same reason why you cannot understand anything when ten people yap at the same time!)

When echoes overlap in time, or when multiple echoes are so closely spaced in time that human ears cannot resolve individual echoes, the effect is called "reverberation". Reverberation is defined as the persistence of sound in a closed, or partially enclosed space after the source of sound has stopped.

 

[Reshma]

Lastly, yes! Denser the medium of propagation-->faster the speed of sound. The speed of sound depends upon the type of medium and its state(solid, liquid,gases).

Examples on Different speeds of sound:
Gases:
331m/s in air at 0 degree celsius
343m/s in air at 20 degrees "
319m/s in argon
Liquids:
1207m/s in ethyl alcohol
1497m/s in distilled water
1531m/s in sea-water
Solids:
6420m/s in aluminium
5790m/s in stainless steel

As you can see here, the speed increases as the density of the medium increases.

 

[Reshma]

Now, I am bit dubious about the speeds in the solid media since my text isn't so accurate. Nevertheless, I hope I solved atleast some of your doubts...

 

[Ouabache]

Lastly, yes! Denser the medium of propagation-->faster the speed of sound. The speed of sound depends upon the type of medium and its state(solid, liquid,gases).

Examples on Different speeds of sound:
Gases:
331m/s in air at 0 degree celsius
343m/s in air at 20 degrees "
Liquids:
1207m/s in ethyl alcohol
1497m/s in distilled water
1531m/s in sea-water

As you can see here, the speed increases as the density of the medium increases.

When I scubadive in sea-water, I cannot discern the direction a sound is coming from. It seems to come from every direction simultaneously. Could the information you have given here, allude to a reason, why humans have trouble determining direction of sound under water? ?

 

[turbo]

When I scubadive in sea-water, I cannot discern the direction a sound is coming from. It seems to come from every direction simultaneously. Could the information you have given here, allude to a reason, why humans have trouble determining direction of sound under water? ?

I'm pretty sure you already know this but we humans have a natural ability to determine the direction from which a sound is emitted, and part of the ability comes from the perception of relative loudness from one ear to the other and part of it comes from an ability to sense a delay between one ear and the other. The very rapid propagation of sound underwater takes much of the delay away, and robs us of some of the perception of direction. Dolphins and whales do not have this problem.

 

[Ouabache]

This wave phenomena is great!

I'm pretty sure you already know this but we humans have a natural ability to determine the direction from which a sound is emitted, and part of the ability comes from the perception of relative loudness from one ear to the other and part of it comes from an ability to sense a delay between one ear and the other. The very rapid propagation of sound underwater takes much of the delay away, and robs us of some of the perception of direction. Dolphins and whales do not have this problem.

Turbo: you're right, I am aware of this and glad that you posted your reasoning on how we perceive direction in air. Triangulation from two receiving antennas (our ears) is an efficient system that our brain handles really well.. Amazing actually

It is also a good deduction, that the rapid propagation of sound underwater is the reason why we lose direction perception. But how fast is too fast?

Is there some way we could find the cutoff speed-of-sound, beyond which we cannot distinguish direction?

Here is the information I have found so far.
In air, sound reaches one of our ears 30μsec before the other.
ref----> http://library.thinkquest.org/28170/36.html and Reshma has told us that the speed of sound in sea-water is 1531m/s . The distance between our ears (as I measure with a ruler) is approximately 7 inches (0.178m).
Also from Reshma's data, sound waves propagate 1531/343 = 4.46 times faster in the ocean than in air.