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Why is a paper falling slower than a heavier object?

  1. Feb 27, 2006 #1
    Why is that a paper which is freely falling down takes a longer time to approach the ground than a heavier object say a ball which is freely falling?
     
  2. jcsd
  3. Feb 27, 2006 #2

    berkeman

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    Staff: Mentor

    The ratio of air resistance to the body's mass. In a vacuum, feathers and paper sheets and bowling balls fall at the same rate.
     
  4. Feb 27, 2006 #3
    You mean because the mass of the paper is less it experiences greater air resistance?
    Can we interpret as follows:
    1.The paper experiences gravitational acceleration
    2.Acceleration due to resisting force acting through the air.
    Then, since the mass of the paper is less it experiences gretaer acceleration due to the resisting force acting through the air(a=F/m).Right?
    The gravitational acceleration is independent of the mass.
     
  5. Feb 27, 2006 #4

    berkeman

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    Staff: Mentor

    The air resistance has nothing directly to do with the mass. The air resistance creates a retarding force to the downward motion of the body. The greather the mass of the object, the better it can overcome this retarding force, and the closer the acceleration will be to the maximum of g.

    It's helpful to work out the math behind this kind of situation, to help convince yourself of what is happening. I did it once after I had (lost) and argument with somebody about bicycles going down a hill. I said (incorrectly) that the mass of the riders should not matter, but it turns out that the masses do matter. Hold the rolling resistance and air resistance constant, and add mass to one rider -- do the calculation to figure out which bicycle goes faster down the hill....
     
  6. Feb 27, 2006 #5
    Let's equalize surface area and material air flow resistance perturbations:
    Take 2 objects, the first being a 1-foot diameter solid sphere of lead, and the second being a 1-foot solid sphere of balsa wood.

    Both objects are then coated on the outside with whatever same substance and polished, such as to render equal any air resistance concerns.

    On an ultra-calm day with no winds, drop them from the same height and at the same time from a tall building.
    Which ball hits the ground first? The lead ball, the balsa wood ball, or both at the same time?
     
  7. Feb 27, 2006 #6

    berkeman

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    Staff: Mentor

    Or a 1-foot diameter balloon filled with air....
     
  8. Feb 27, 2006 #7
    A good extension, though I would not use a gas balloon in a serious experiment even in a calm wind environment due to the gases ultra-sensitivity and commensurate volume displacement from thermal influence which could affect the wind drag.
    In addition, even in a calm wind, an ultra light balloon could be seriously influenced by even the smallest whisper of wind.
    Nonetheless, your point is well taken.
     
  9. Feb 27, 2006 #8
    Here is something that may help you see what all the fuss is about... the Apollo 15 Hammer-Feather Drop experiment - on the MOON!

    Go here jrm:
    http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_15_feather_drop.html

    -LD
     
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