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The Dopper Effect?

  1. Nov 14, 2003 #1
    I thought I would present this before I posted it on the mandatory
    participation class ‘Discussion Board’. Any suggestion would be
    appreciated. I'm sure you all have heard it before.

    The question is- “Does wind affect the Pitch of the factory
    whistle you hear on a windy day?"
    The assignment illustration
    shows a person down wind cupping his ear toward the sound of the
    whistle .

    My answer- No it does not (although there might be a delay in
    hearing the sound by the one who is up wind of the whistle).

    My reasoning- Pitch is a measure of the number of vibrations
    (waves) that is experienced in a particular period of time (seconds),
    through a particular medium (air) at a particular point. This
    normally is represented in Hz (vibrations or wave lengths ‘lambda’
    per second). The Doppler effect (which is really what the question
    is a test of) is where differently orbital positioned receivers,
    experience different pitches (Hz), after the sender has transmitted a
    wave with a constant wave length and speed (Hz), while either the
    receivers or the sender or both are in motion. If both the sender,
    and the receiver are stationary, all receivers will experience the
    same Pitch of vibrations that the sender is producing. This would be
    true whether the medium (air) is in motion or not.

    Further Critical Thinking- If (by chance) the receiver was upwind
    and the air was blowing at or faster than the speed of sound, would
    a receiver upwind of a sender ever hear the sound?

    How far off base, with any of this, am I?
  2. jcsd
  3. Nov 14, 2003 #2


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    Homework Helper

    Yeah, I think you're right. If I remember correctly, as long as the source and observer have no relative velocity, there is no frequency shift (and, of course, both stationary constitutes no relative velocity). I think is is basically what you said, but I wanted to make sure you understood that they could both be in motion as well. In fact, as far as waves go, with respect to the medium, the source and observer are both in motion.
  4. Nov 14, 2003 #3
    The moving medium was the kicker that caused me to question my reasoning. I’ve thought about it quit a bit, and finally decided that the medium effects only the time in which whatever ‘Hz’ of the wave is, is initially received by the receivers. I cannot see where the constant airflow would affect the ‘Pitch’.
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