Something I thought was interesting

[MetalDave]

Sound is actually the result of “an organized disturbance of pressure in the air. The human ear is capable of perceiving sounds which are so weak that they cause the ear drum to displace by less than the size of a hydrogen atom which has a diameter of about a billionth of an inch. Such a faint sound has a pressure disturbance of about a billionth of one atmospheric pressure (which is about 14.7 pounds per square inch or 0.1 MPa). Extremely loud sounds which normally produce pain, have sound pressures of about one thousandth of an atmosphere.

[EnSkorSang]

Interesting...I sometimes try to define what sound actually is....in geophysics a seismic wave is pretty much identical to a sound wave - they are both pressure waves, in fact most geophysicists talk about 'sound waves' when referring to seismic waves. However you can't 'hear' a seismic wave, but it can be recorded by a seismometer measuring ground displacement - is this sound or not?
My common answer is - i dont care

[MetalDave]

Not unless it is disturbance of pressure in the air. If the ground moves enough to cause a disturbance of pressure in the air of .1 MPa, you will hear a sound. I would say that is the point where seismic becomes a sound wave.

[Ruzz]

Originally Posted by MetalDave

Not unless it is disturbance of pressure in the air. If the ground moves enough to cause a disturbance of pressure in the air of .1 MPa, you will hear a sound. I would say that is the point where seismic becomes a sound wave.

Doesn't have to be air - sound travels through other media too... like water (actually, it travels faster under water, and generally, the denser the material the better - up to a point). So, I'd guess any medium that can support the transmission of an oscillation, is capable of transmitting sound as long as you can connect that medium to the source and your ear. Like air. Or water. Or Beer

[String7th]

[MetalDave]

It is really quite simple. If you can hear it..... it is sound. The atmospheric pressure has to be greater than .1 to be able to hear it under water. But yeas you can hear under water. You can hear a long ways away under water. The more dense the medium the faster the sound will travel. If the air is humid sound will go faster than 1100 FPS. Thus changing frequencies.

[brandondrury]

The way I understand it, it's all just waves. Light is just a wave as well, right? It's just way up higher on the scale. Our ears hear the 20-20k stuff. Our eyes see the INSERT EYE FREQUENCIES HERE frequencies.

Or am I wrong?

Brandon

[MetalDave]

Actually light is particles and waves. These particles are called photons. They stretch millions of miles. One photon can be here and still on the sun at the same time.

Frequency of visible light waves
= velocity of light / wavelength
= (3 x 10^8) / (4 x 10^(-7) = 7.5 x 10^16 Hz
to
= (3 x 10^8) / (7 x 10^(-7) = 4.3 x 10^16 Hz


The velocity of sound in air is constant, 1100 ft/sec. Therefore it makes it fairly easy to determine the wavelength of a sound wave if the frequency is known. Since the velocity (1100 ft/sec) is constant which is the product of the wavelength and the frequency, it argues that if the value of the frequency is large, the value of the wavelength must be small. If the value of one is double the value of the other is halved. For example, if the frequency is1100 Hz, then the wavelength would be 1 ft. If the wavelength is doubled, 2200 Hz, then the wavelength is 0.5 ft. It will be the same effect on the frequency if the wavelength were doubled or halved.

Does this help us in engineering good records? I think not! Just thought the first item was interesting 1 billionth of an inch......... WOW!!!

[String7th]

[EnSkorSang]

Light is actually neither a particle or a wave...its a mystery. It can just be thought of as particles and waves as the properties of both of these can together explain the properties of much of light. Photons is physicists trying to hoodwink you , its a convienient way to describe the little 'packets' of energy which in some situations explain what the frik light is doing.

A sound wave IS a seismic wave - they are all pressure waves (when thinking of light as a wave, it is an electromagnetic wave). The question is...just because you cant hear the pressure wave in some medium, is it still sound? which is entirely the same question as if a tree falls and there is no one to hear it, does it make a sound? which is best left for very very very bored people to think about.....