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Homework Help: Conceptual questions:Newton's Laws(Grade 11)

  1. Sep 8, 2008 #1
    Any help will be appreciated:)

    1) When a soda bottle is opened,gas bubbles rise up. Will they continue to rise if the bottle slips and starts falling?
    (Note:-I've noo idea what they mean!!!!)
    2) An hourglass is kept on a weighing machine. Will the weight recorded be more if all the sand is in the lower compartment,or if sand gradually falls from one compartment to the other?
    (Note:- I think this has something to do with impulse. Weight recorded should be more in the 2nd case,because an additional impulse is exerted on the weighing machine by the falling sand. I can be completely wrong of course,hehe.)

    Please help!!!!
  2. jcsd
  3. Sep 8, 2008 #2
    1) If you don't know what the questions means ask your teacher what he thinks it means! Anyway, the question isn't clear. Does it mean: will the bubbles 'continue to rise' (i) relative to the falling bottle, or (ii) relative to you, stood standing there. Until you know this, you can't answer the question. So teacher is being either (i) unfair in setting a trick question, or (ii) thick.

    2) Try a google search on the key terms of the question. I tried 'hourglass weighing machine', and obtained:


    There are many more :-)
  4. Sep 8, 2008 #3


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    Science Advisor

    Actually both of those problems have to do with "closed systems". The bottle, soda, and bubbles are a closed system. what happens inside the bottle is not affected by the motion of the bottle itself. The hourglass is a closed system. What weight is registered is not affected by what happens inside the hourglass.
  5. Sep 9, 2008 #4
    Thanks alot,both of you:)
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