If two identical tuning forks are struck, then one placed on a moving stage, constant speed away from the observer, and the other is left stationary. What would the obsrver hear, why?
Thank you!
2006-10-17 01:17:36 · 4 answers · asked by miledi111 1 in Science & Mathematics ➔ Physics
You will hear the stationary because the other one is fadeing out
2006-10-17 01:34:42 · answer #1 · answered by mms 3 · 0⤊ 1⤋
The observer would hear "beats" or pulsations of sound as the two tones would become slightly out or tune. This also happens if two guitar (piano, etc.) strings slightly out of tune are plucked together. The sound waves of the strings periodically reinforce and cancel each other as they pass in and out of phase. The moving tuning fork produces the correct tone but the sound waves are stretched in the direction of motion causing the wave peaks to spread and lowering the tone heard by the stationary observer in accordance with the Doppler effect. The beats have their own frequency which is the rate that the phases agree. Piano tuners often need to tune three "identical" strings in the upper register (that triple the sound output) and they use beats then the lack of beats to ensure good tuning. Piano tuners can even hear the beats within the harmonics (overtones) of different notes to get the right "color" for the sound.
2006-10-17 08:33:27 · answer #2 · answered by Kes 7 · 1⤊ 0⤋
This is a guess, mind you.
As the moving tuning fork moved away, the Doppler effect would cause its pitch to drop very slightly. This would put it slightly out of phase with the stationary tuning fork.
So what you would hear would be a sound that faded in and out in a kind of tremolo effect.
2006-10-17 08:28:23 · answer #3 · answered by langdonrjones 4 · 1⤊ 0⤋
The one moving away would sound at a lower pitch due to the Doppler effect
the picture here:
http://en.wikipedia.org/wiki/Doppler_effect
shows it visually.
the sound waves would be effectively longer as the source moves away.
Think of it as the source 'stretching' the waves as it moves away.
if it moved towards you then you could think of it as 'compressing' the waves.
but this is only part of it (I'd forgotten about the stationary one)
Interference will take place
http://en.wikipedia.org/wiki/Interference (see the heading Constructive and Destructive interference)
and the sound volume will increase and decrease.
draw one wave on paper, and another of longer wavelength on tracing paper, and slowly slide one over the other.
the volume of the noise will be equal to the sum of the two waves.
[PS vote for Langdonrjones as I'd missed a bit!!]
2006-10-17 08:25:16 · answer #4 · answered by Me 3 · 1⤊ 0⤋