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Thread: Falling objects

  1. #1 Falling objects 
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    If you drop a 50 pound ball and a feather (not in a vacuum), the ball will hit the ground first.
    But, if you drop them in a vacuum, they both hit the ground at the same time.
    The only difference is the vacuum (and air resistance).
    So, if you drop two identically shaped balls, but one weighs 50 pounds, and one weighs 50 ounces (not in a vacuum), why does the heavier one hit the ground first (since they both now have the exact same air resistance as in the vacuum)?


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  3. #2  
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    Quote Originally Posted by Speedy View Post
    If you drop a 50 pound ball and a feather (not in a vacuum), the ball will hit the ground first.
    But, if you drop them in a vacuum, they both hit the ground at the same time.
    The only difference is the vacuum (and air resistance).
    So, if you drop two identically shaped balls, but one weighs 50 pounds, and one weighs 50 ounces (not in a vacuum), why does the heavier one hit the ground first (since they both now have the exact same air resistance as in the vacuum)?
    The acceleration due to gravity alone is indeed the same for both balls. And, the force due to air resistance is indeed the same for both balls, as they are of identical shape. But the two balls are of unequal mass, so that equal air-resistance-force produces unequal accelerations. That's where the asymmetry comes into play.


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  4. #3  
    Moderator Moderator Janus's Avatar
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    First examine why they would fall at the same rate in a vacuum. The force acting on the 50 lb ball due to gravity is 800 times the value of the force acting on the 50 oz. ball. But its mass, and thus its resistance to being accelerated is also 800 times greater.

    Now, with the same sized balls in air, the force due to air resistance is the same for both, but their masses and their tendency to have their velocity effected by that force still differs by a factor of 800.

    Let's put it this way, would you expect the same size of parachute to be just as effective in slowing the fall of that 50 lb ball as it would be at slowing the fall of the 50 oz ball?
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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