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Will weight of flying mosquito in a jar affect its weight ?

  1. Sep 4, 2011 #1
    As a part of an experiment,..............
    a scientist put 100 mosquitoes in a jar and shut it..... When he weighed the jar, while the mosquitoes were sleeping on the base of the jar, the weight came out to be 250 g........... Then, he shook the jar and the mosquitoes started flying inside it. He once again weighed the jar now and noted the reading....... What can be said about the reading – will be equal to 250 g or less than it or more than it?
     
  2. jcsd
  3. Sep 4, 2011 #2

    Doc Al

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    Staff: Mentor

    What do you think? Consider the center of mass of the system.
     
  4. Sep 4, 2011 #3
    Can someone explain it please?
     
  5. Sep 4, 2011 #4
    The jar would be a closed system when the mosquitos fly they apply an opposing force equal to the force needed to achieve flight therefore the jar will still read 250 g
     
  6. Sep 4, 2011 #5

    rcgldr

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    Homework Helper

    As long as the center of mass of jar and mosquitos is not accelerating vertically, the total weight remains the same. Note that if the jar only contained air, then there would be a pressure differential within the jar, lower at the top, higher at the bottom, producing a net downwards force on the inside of the jar exactly equal to the weight of the air in the jar. As an example, filling a scuba tank with 80 cubic feet of highly compressed air will increase it's weight by 6 lbs, the weight of the 80 cubic feet of air at sea level and 1 atm pressure. When the mosuitoes are flying, or if a tiny balloon was hovering in the jar, the pressure differentital of the air is increased so that the net downwards force inside the jar exactly equals the total weight of the air and anything in the air, such as the mosquitoes and/or a hovering balloon, as long as there is no vertical component of acceleration of the overall center of mass.
     
  7. Sep 5, 2011 #6
    The agitated mosquitoes heat themselves up by flying around, and radiatively cool, gradually losing mass as they get skinnier. So the total weight will be slightly less as the radiative energy escapes into the space surrounding the slightly warmer jar, and to calculate an answer you would need to know how much radiant heat energy is being supplied by each mosquito. Even if you neglect this minor effect, there will be tiny fluctuations depending on the total vector sum of the instantaneous flapping force, so you have to supply more information on the direction and acceleration of each individual mosquito. Therefore no answer can be supplied - you can tell your teacher I said so.
     
  8. Sep 5, 2011 #7
    Now theres an answer I never would have considered lol.
     
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