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Name:  Gary S.
Status:  other
Age:  20s
Location: N/A
Country: N/A
Date: 2000-2001
Question:
Reciently I was watching waves in the water and wondered why sound has a set speed.

Replies:
On a related note I was wondering if sound can only be created by an object that is travling faster than the speed of sound for a short period of time and how do tital waves travel as fast as they do.

The speed of sound is NOT constant. The speed depends upon its frequency, the medium through which it is traveling, and whether the waves are transverse [vibrations perpendicular to the direction of propagation], or compressional [vibrations in the direction of propagation].

Sound need not be produced by oscillations traveling at speeds greater than the speed of sound in the medium. In fact, that is the exception [shock waves and/or cavitation] to the rule. Usually the medium begins to vibrate at the frequency in resonance with the sound source.

Tsunami [tidal waves] are caused by earthquakes or volcanoes. I would suggest a websearch on the term "tsunami" would result in a lot of info about their dynamics. That is not my area of expertise.

Vince Calder

Gary,

Sound does not actually have a "set" speed. It has a specific speed in each medium through which it travels. In air, sound travels at about 350m/s. In warmer air, it travels faster. In steel, sound travels at 4,500 m/s. Sound travel is much like waves traveling through a slinky. Vibrating molecules cause neighboring molecules to vibrate. This continues on through the material. Because steel molecules are so tightly locked together, very little time is required for one molecule to affect another. In air, it takes a little longer for the signal to pass.

Any vibrating object can create sound waves. If the vibration frequency is too slow(less than 20 cycles per second), our ears will not respond to it. If the vibration frequency is too fast(more than 20,000 cycles per second), our ears will not respond. An object moving back and forth 20 times per second is producing a low frequency sound wave. This is about the frequency of a bass drum. It has nothing to do with meters per second that the vibrator moves.

A tidal wave travels at about the same speed as the non-tidal waves. There is no great increase of speed.

Dr. Ken Mellendorf


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