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How does a tin can phone work?

  1. Feb 5, 2010 #1
    Hi, I'm just wondering what the physics are behind why a tin can phone works (two cans connected by a string, one speaks into one can, and the other can hear it in the can on the other end.)

    Is it simply that when one person talks into his/her cup, the bottom of the cup vibrates back and forth with the sound waves and the vibrations travel through the string by pulling the string back and forth, therefore, the bottom of the second cup should start to vibrate back and forth just like the bottom of the first cup is vibrating, producing sound waves. The second person can hear the sound waves and can therefore hear what the first person says.

    But is it really that simple? And how exactly to the vibrations of the string transport the actual sound waves themselves along the way?
  2. jcsd
  3. Feb 5, 2010 #2


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    What do you believe to be the difference between the "sound waves" and the "vibrations of the string?"
  4. Feb 5, 2010 #3
    mmm, good point I guess the only real difference is that the shape of your mouth, tongue, teeth, etcetera, is part of what makes words as opposed to just ambiguous tones or pitches, so how does that translate across a vibrating string? Do all these things I just mentioned effect the actual vibration itself? In other words I understand how the pitch and timbre travel through the string, as it's vibrating at the same rate at which the sound wave being produced is, but where does the actual diction of the language occur and how does that travel through the string?

    Perhaps I'm just making this more complicated than it is? haha
  5. Feb 5, 2010 #4


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    The physiology of producing human speech has nothing to do with your actual question, so you're focusing on the wrong aspect. The fact of it being human speech also has nothing to do with sound being transmitted (you could transmit non human sounds using this same method). Maybe that's where you are getting hung up.

    I asked the original question because it appears you are treating "sound waves" and "vibrations of the string" as different things. Really they are both just vibrations, the only difference being which medium they are passing through (air, string, can) at the time.

    I believe your latest response shows a lot of confusion on defining "sound waves" (it appears you define "sound waves" as limited to human speech), and thinking there is something special about sound transmission itself that makes human speech something special. The fact is that human speech is simply an adaptation that allows us to manipulate the world around us (specifically the air we breathe) for our benefit (communication).

    Summary- There is nothing special about a couple of cans and a string to be able to convety some sort of "magic" that is human speech. It's simply longitudinal vibrations through certain mediums and in a certain frequency range that permits an auditory response in the person on the other end.
  6. Jul 30, 2010 #5
    Im just going to put out a guess.. Both tin cans are identical in shape so they both encode and decode the same way. The first one simply converts the sound into a vibration in the string, and the second cup converts it back.. An example of this could probably be sending and receiving radio waves and using a headphone as a mic ( just plug the headset into the mic port xD)
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