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Sound Problem

  1. Feb 6, 2005 #1
    I read in a magazine the other day about a problem...

    You have a cup of tea. You start clicking with your tea-spoon on the cup and you put in som sugar. The sound of the clickings will change. Why?

    I guess that the sugar changes the density of tea, changing the speed of the soundwaves, chaniging the sound frequency which will ultimately change the sound of the clickings...

    Not a scientific explanation, but am I correct?
    Anyone have a better, more scientifc, answer?
     
  2. jcsd
  3. Feb 6, 2005 #2

    krab

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    You are right on. Mainly the density chang is due to micro-bubbles that get mixed in with the sugar. Eventually, the effect disappears.
     
  4. Feb 17, 2005 #3

    jp

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    My old teacher actually worked with the guy (sorry, I forgot the name) who posted that article in the magazine. I believe he refered to that phenomenon as "mass loading". I can't remember from top of my head, but it's got to do with density as you guessed. After all the suger dissolves into the tea, the sound will come back to the original pitch. (The pitch difference b/w before and after adding suger is one octave)
     
  5. Feb 26, 2005 #4
    but why will the sound return to its original pitch, when dissolved?
    the density wont return so the sound shoudnt either....
    If not for the theory about small buybbales being created....

    I'm thinking of doing an experiment on this for my Physics Assessment... What kind of experiment should i do... thinikng of having a frequency detector noting the frequence, and how it chnges when the sugar is inserted in the cup.. I will click with the spoon all the time and note the frequencey.. do you guys think the change in frequenvcy will be significant enough to be detected by such a basic experiment...

    any other idea for experiment, or a way to show the change in sound?
     
  6. Mar 14, 2005 #5
    sorrry to double post but I needed to get his thread up... need answers to my previously asked questions as I need to do the experimenton thursday...
     
  7. Mar 14, 2005 #6
    Strid,

    To gleen the most of this concept, cross examine the experiment in any way you can think of.

    Start with questions.. tea is usually made hot, and hot tea also dissolves suger better than cold. Did they take before and after temperatures? If not, do 1 cup the way they did it, and another with a constant heat source. (heat will vary the speed of sound). Also do a cup with 10 teaspoons, and 1 with more sugar than tea. Does the viscosity of the tea also affect the sound? If you can ask questions that were not answered in the first experiment, and then answer them with your experiment, then you have done good science.

    And don't forget the standard Teachers' question: did you bring enough for everyone?

    TRoc
     
  8. Mar 15, 2005 #7
    Did the experimnet today... checked whether the freuqncey changes or not... I didnt notice any change at all... Though I recorded the change in sound which is quite clear... but it COULD be the fact that i clicked irregularly on the cup... :(
     
  9. Mar 19, 2005 #8
    I just did some experiments, and have some more questions on my results...

    as i put in the salt the pitch decreased for a while before increasing again just below the original pitch...

    the graph, with time as x-axis and pitch as y-axis, would look something like this...


    xxxxxxx................................................................
    ..........x...........................xxxxxxxxxxxxxxxx............
    ...........xx.....................xxx.................................
    .............xx...............xxx....................................
    ...............xxx........xxx.........................................
    ..................xxx.xxx..............................................
    .....................xx...........................................
    ................................................................

    Why does the pitch almost return to its original pitch??
    The result was clearer with hot water, probabaly becasue o it solves the salt better...
     
  10. Mar 19, 2005 #9
    Air is dissolved into the (hot?) liquid with the salt creating microscopic air bubbles causing the pitch to drop rapidly. Then the bubbles dissolve into the liquid causing a rise in pitch but because the salt has now dissolved too, the liquid is denser and the pitch shan't rise as high as it was at the beginning.
     
  11. Mar 20, 2005 #10
    yeah.. it seems to be something like that.. but I dont get toally how the air gets into the water.. is the air "in" the salt?

    Also.. could someone explain thoroughly why the pitch drops rapidly as the microbubbels are cretaed?
     
  12. Mar 23, 2005 #11
    This is something you can actually see. If you take a clear glass, fill with pure, warm water and pour a tablespoon of salt into it and stir, you will see the liquid turn slightly cloudy, until most of the salt has dissolved, then it will regain its clarity. This will coincide with the pitch shift. I think the air is in between the salt crystals although it may also be trapped in the salt crystal lattice.
     
    Last edited: Mar 23, 2005
  13. Mar 29, 2005 #12
    just thought of a thing...

    I got confused when I just thought of that salt has higher density than water while air has lower....

    So if the pitch at the end of the experiment is lower it means that the increased density has resulted in lower pitch...

    But than, the airbubbles, that have lower density should resullt in a higher tone, or??

    Could someone, also explain thouroghly why the pitch drops as the airbubbles are created.
     
  14. Apr 8, 2005 #13
    There may be more at play here than just densities. There are four different states of matter here: solid (salt); liquid (water); gas (air bubbles); and plasma (I think salt water fits the definition of plasma).
     
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