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Question for my Physics Project.

  1. Dec 7, 2013 #1
    1. The problem statement, all variables and given/known data
    Some disease-causing bacteria are carried by the air. Why don't these organisms fall to the ground as other objects?


    2. Relevant equations
    Drag equation might be useful here (I think)


    3. The attempt at a solution
    I think it is because of air resistance. It is the force that are in opposition to the relative motion of an object moving through the air. It depends on velocity. It is calculated by using the drag equation.
    However, I couldn't really figure out the connection between these.

    Hi I am Kuzey Cem and I am a 12 year old student in Turkey. I am interested in any science, especially Physics and Biology.

    1. The problem statement, all variables and given/known data
    Which normally requires more work: pulling the piston of a water pump out of the cylinder or pushing it back in?

    2. Relevant equations



    3. The attempt at a solution

    I think it is related to pressure, and also force. But I don't know how pistons really work.

    1. The problem statement, all variables and given/known data
    When you wipe your feet to the carpet, how do your voltage and that of the carpet change?


    2. Relevant equations



    3. The attempt at a solution
    I found out that this is about static electricity and charges.
     
    Last edited: Dec 7, 2013
  2. jcsd
  3. Dec 8, 2013 #2

    Simon Bridge

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    Welcome to PF;
    i.e. what makes things float?

    Some other force opposing gravity is a good start, and drag is one of them.
    You correctly observe that drag is proportional and opposite the velocity.
    Consider though, if something is floating, as opposed to falling, then what is it's velocity like?
    Therefore, how much drag force is acting?

    Are there other things that can make something float?

    ... Then I suggest you go find some pictures of pistons in operation.
    Seriously - this is a basic concept that will be used over and over again so you need to get a feel for it.

    The pump is a hollow cylinder with a hole in the bottom, with a valve so water can only flow inwards.
    The piston part is a solid cylinder that fills the inside - but can slide up and down.
    You pull up on the piston, the piston pulls water into the chamber. When it is all the way up, you push down on the piston, and water flows out another hole, through another valve - which allows water to only flow out.
    What determines the work done during each part of the cycle?
     
  4. Dec 8, 2013 #3

    mfb

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    They are not floating in the same way hot-air balloons do. They are just tiny, so air resistance is extremely relevant, and the air in our environment is always in motion.

    Correct.
     
  5. Dec 8, 2013 #4

    Simon Bridge

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    Yes - there are forces at work besides buoyancy ...
     
  6. Dec 12, 2013 #5
    So if the bacteria is flowing, it has a low velocity? Is that correct?
     
  7. Dec 12, 2013 #6

    mfb

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    Staff: Mentor

    A low velocity relative to the air, yes.
     
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