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Question about loudness of sound

  1. Feb 10, 2010 #1
    I recently read an experiment from a science book for elementary school students. Basically, it asks students to compare the loudness of sound produced by shaking the small plastic bottles containing different amount of red beans. There're altogether 4 plastic bottles, filled with red beans to 1/4, 1/2, 3/4, 4/4 of the volume of the bottle. Each bottle is then shaken with the same "amount" of energy (e.g. 3 times), then students are asked to compare the loudness of the sound produced.

    What do you guys think? Which of the bottle will produce the loudest sound?
    Actually, do you guys think this experiment makes sense scientifically?

    Thanks a lot.
    Last edited by a moderator: Feb 16, 2010
  2. jcsd
  3. Feb 11, 2010 #2


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    Welcome to PF, C.S.
    In my experience, and through common sense reasoning, the emptier the bottle the louder should be the sound. To a limit, of course. The bottle is essentially an echo chamber. More beans means less air space for resonance to occur in. Experience-wise, I'm going by medicine bottles. A full bottle doesn't rattle nearly as much as a half-full one, and a quarter-full one is even louder. Once below that level, the shortage of pills causes less impact sound to start with. There is probably some formula to calculate the details, but I have no idea of what it might be.
    By the bye, please use standard black text. Some of us with old eyes find colours hard to deal with.
  4. Feb 11, 2010 #3
    Thank you so much for the explanation, Danger.
    And I'm really sorry about the colour of the text.

    But I have a question, does the volume of the air space within the bottle affect the frequency (the pitch) or the amplitude (the loudness)?
  5. Feb 12, 2010 #4


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    It should certainly affect the pitch. The enclosed space of the bottle is effectively a leaky resonating chamber. The frequencies of waves that exist in the chamber are determined by the physical dimensions of the chamber and the properties of the walls. Given that the bottle's walls behave the same regardless of the bottle's size, a large bottle will allow lower frequency modes to exist. So the larger the bottle, the more lower frequency sounds that can be sustained. Since the bottle is asymmetric though, how you shake the bottle may affect the pitch as well. However, I would expect that the random nature in how we shake things will probably minimize this effect.
  6. Feb 12, 2010 #5
    It doesn't make complete sense as it stands at the moment.
    An experiment of this sort at elementary level (and any other level for that matter) should have a clearly defined teaching aim. I'm not sure what that is in this case. In addition, what should the children learn and take away from from this?
    The only science I'm happy with in what I read is that beans make a sound when shaken in a container. As for loudness, that is very subjective at any age; especially in youngsters.
    How, exactly, are they supposed to "compare"?
    "Amount of energy" in the shaking of the beans is possibly the worst part of this. There is no correlation that can be guaranteed between a) the number of shakes and the "energy", and b) the same number of shakes from different children.
    As such, the only scientific conclusions I would expect children to draw from this would be rather vague notions to the effect that the sound produced "changes" when different amounts of beans are used. It may be possible to come to some conclusion about which of the 3 situations is the loudest, but then what scientific principle have we taught?
    This goes back to my 1st question. There should be a specific aim stated for this activity in the teacher's guidance notes. I would be interested to know what that is.
  7. Feb 12, 2010 #6


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    Actually, there was no mention of a teacher. C.S. said that s/he ran across it in a book. Should that book be utilized by a teacher, then s/he would be responsible for interpreting both the question and the posited answers.
    As presented, I think that it's an interesting subject that invites just such questioning as you have brought forth. The mere fact of your posting supports that. By your protestation, therefore, you are validating the original question. Ironic, ain't it? :wink:
  8. Feb 12, 2010 #7


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    I think the emptier bottle would be louder, but for a different reason. If the bottle is mostly empty, with the same force shaking the bottle, the beans will get a higher velocity and impact the walls of the container with a larger force. Also, when the container is more full, the beans on the outside will absorb some of the sound energy from the beans in the middle.

    I think this is a useful experiment for kids because it is a thought experiment that you can test with observation. It teaches kids to think about physical processes and validate their theories, even if the specific excercise itself doesn't necessarily teach anything useful.
  9. Feb 12, 2010 #8
    Well, as it was an activity from a science book for elementary school students, it should have been written with a clear educational aim, and probably assuming a teacher would be facilitating the learning. Most modern books come with teachers' notes.
    If it was a fairly recent book (ie not about 50 years old!) it would almost certainly have the relevant information. As I say, I would be interested to know what that aim was.
    If it was not a specific cognitive aim to do with the nature (loudness?) of sound, it could also be a more general affective aim to do with stimulating curiosity etc etc.
    The question was about whether the activity makes sense scientifically. Without the stated scientific learning aim of the experiment, it's difficult to say.
    The activity, in and of itself, may well be worthwhile. The scientific sense, from an educational perspective, depends on how its managed and how the children's questions are dealt with.
    This was a (very) long winded way of saying to the OP; more information needed. :wink:
  10. Feb 16, 2010 #9
    Thank you so much everyone for the replies. All of you helped me to understand this experiment a lot more.

    Somehow, I think this experiment is pretty difficult for 2nd an 3rd grade students. It's not only because of the concept of sound is difficult, it is also because the pitch and the loudness of the sound produced by the beans in the bottles change at the same time, making it difficult for students to make comparison.

    The aim of the experiment, as stated in the book, is "how to produce the loudest sound". However, this aim is pretty vague and scientifically not specific to me. Maybe its aim should be just a more general affective aim as Stonebridge suggested.

    I think QuantumPion is also right that this experiment provides kids with an opportunity to understand how scientists make hypotheses (yes, one of the things that kids have to do before actually carrying out the test is to make “guesses”) and carry out tests to verify them.

    Indeed, what worries me most about this experiment is whether misconception about the loudness of sound will be delivered. That why I asked in the beginning whether you guys think this experiment makes sense scientifically.

    By the way, does anyone agree with QuantumPion’s explanation with velocity and absorption of sound?
  11. Feb 16, 2010 #10
    Oh by the way, Stonebridge, I guess we can't compare the experiments carried out by students are the elementary level with those carried out by scientists. You know, many of the schools don't even have money for a decibel meter. It's just very important for the teachers to remind students to try their best to use the "same amount of energy" to shake the bottles.
  12. Feb 16, 2010 #11
    Indeed they should, but there is no correlation between "same amount of energy" and shaking "3 times".
    I have no idea what scientific principle that is attempting to teach.
    Even at this age, there should be some concept of the energy in the shake being more to do with how "hard" or "fast" you shake the beans, rather than how often.
  13. Feb 16, 2010 #12
    I really don't want to get into politics here, but there are statements here that do relate to science education and thus very much relate to the FUTURE of science.

    One idea is that since these are just kids that the "science" experiments they perform don't have to make sense. Obviously just the opposite is true. One would really want to get down to the essence of science principles rather than just sow confusion. One problem I imagine is that it's probably harder to create an effective simple experiment that makes valid points than it is for real scientists to just buy a bunch of expensive gear and take data. One would rather have Nobel prize winners designing school experiments than some text book authors.

    Another idea is that somehow money = education. I don't know of ANY school that can't afford a decibel meter! I know of many that PRETEND to not be able to afford them. These devices are readily available from Radio Shack well within any school budget. Hell even the teacher could afford one on their pay. But buying one is not allowed because it doesn't come from a school supply house that gives kickbacks etc. Many school systems are like ours. It could be floated down the river on a sea of $20 bills based on the money they waste, but still rates lowest in the state. And that's because science is done between the ears not with money.

    And lastly, a good experiment doesn't "remind" students to "use the same amount of energy" it would set up some way to insure that it happens. Can you think of ways to insure that? Obviously psychological measurements such as doing things you "think" are equal" are the VERY thing you want to teach the students to AVOID. Our senses and minds often play tricks that real measurements reveal. THAT should be the lesson.

    Am I banned yet?
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