Sound waves, and bones, ear (BR physics)

anbuitachi

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  1. Attending Physician
    Ok one of the questions in BR physics said that: We hear our voice with a lower frequency than we'd hear if we tape our voice and replay it because bone transmits lower freq better than air.

    The question below that says human ear is sensitive to frequency and intensity only but not wavelength.

    Does this mean that even if sound goes through bones with high velocity, the ear disregards the wavelength of the sound and only cares about frequency? Cause I dont understand why we hear lower frequencies if it is transmitted through the bone since sound in bone travel MUCH faster than in air/water...

    Another question:
    Why is active radar radio waves double compressed (double doppler shifted)?

    Thanks
     
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    dingyibvs

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      Ok one of the questions in BR physics said that: We hear our voice with a lower frequency than we'd hear if we tape our voice and replay it because bone transmits lower freq better than air.

      The question below that says human ear is sensitive to frequency and intensity only but not wavelength.

      Does this mean that even if sound goes through bones with high velocity, the ear disregards the wavelength of the sound and only cares about frequency? Cause I dont understand why we hear lower frequencies if it is transmitted through the bone since sound in bone travel MUCH faster than in air/water...

      Another question:
      Why is active radar radio waves double compressed (double doppler shifted)?

      Thanks

      Explanation:
      For the first question, you're dealing with two different concepts. Yes, sound does travel faster in solids such as bones, but it does NOT affect the frequency of the transmitted sound. Neither does air for that matter. Bones do not transmit lower frequencies better because it changes the frequency of the sound transmitted, it does so by keeping the INTENSITY of the lower frequencies better. In air, the intensity of lower frequencies drop much quicker than it does in bones, but the frequencies themselves do not change.

      Example:
      Let's say you sing a bass note. You'll hear it quicker if it's transmitted through a bone rather than air, but you'll hear the same exact note(i.e. the same exact frequency). However, the note will be LOUDER if you hear it through a bone as opposed to air. The intensity changes, the frequency doesn't.

      Now, for the second question: I assume that an active radar is one that is moving? If that's the case, then the frequency changes because the source is moving, and the frequency also changes because the target is moving too, thus the doppler effect is doubled(not numerically doubled, just that you have to count it twice).
       

      anbuitachi

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      1. Attending Physician
        Explanation:
        For the first question, you're dealing with two different concepts. Yes, sound does travel faster in solids such as bones, but it does NOT affect the frequency of the transmitted sound. Neither does air for that matter. Bones do not transmit lower frequencies better because it changes the frequency of the sound transmitted, it does so by keeping the INTENSITY of the lower frequencies better. In air, the intensity of lower frequencies drop much quicker than it does in bones, but the frequencies themselves do not change.

        Example:
        Let's say you sing a bass note. You'll hear it quicker if it's transmitted through a bone rather than air, but you'll hear the same exact note(i.e. the same exact frequency). However, the note will be LOUDER if you hear it through a bone as opposed to air. The intensity changes, the frequency doesn't.

        Now, for the second question: I assume that an active radar is one that is moving? If that's the case, then the frequency changes because the source is moving, and the frequency also changes because the target is moving too, thus the doppler effect is doubled(not numerically doubled, just that you have to count it twice).

        I'm kind of confused. If sound moves faster in bone and v=f lambda, so if v goes up doesn't f or lambda have to go up? If you are saying frequency is the same does that mean wavelength increases?

        and for the 2nd question, the radar is stationary. actually there are two questions that asks this basically, one mentions specifically active radar while the other just says "radio wave reflected off a moving object" for radars. in both, the doppler is double counted...
         

        puravida85

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          I'm kind of confused. If sound moves faster in bone and v=f lambda, so if v goes up doesn't f or lambda have to go up? If you are saying frequency is the same does that mean wavelength increases?

          and for the 2nd question, the radar is stationary. actually there are two questions that asks this basically, one mentions specifically active radar while the other just says "radio wave reflected off a moving object" for radars. in both, the doppler is double counted...

          Yes, when a wave travels to a different medium, its wavelength changes with its speed but the frequency remains constant.

          As far as the doppler question goes, you should focus on how to apply the scenarios to the actual doppler equation. Without specifics, I can't help you here.
           
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