Re: Physics - biking question

Discussion in 'Cycling Equipment' started by [email protected], Oct 3, 2004.

  1. On Sun, 03 Oct 2004 19:16:23 GMT, Retro Bob
    <[email protected]> wrote:

    >OK, all you amateur physicists:
    >
    >If a 155 pound mass (me) is traveling at 10 mph (on bike) and I
    >strike an object dead on with my shoulder (roughly 2 sq inches) -
    >what the load presented by my shoulder to the object.
    >
    >A rough calculation of 150lbs concentrated into 2 sq inches tells
    >me that the static load would be 75 lbs/inch... but obviously
    >the 10 mph would be the key here... and I forgot more physics than
    >I ever really understood.
    >


    Dear Bob,

    Assuming that whatever 1.4 x 1.4 inch surface that you run
    into is not moving toward or away from you . . .

    The mass and nature of whatever you hit will affect the
    outcome.

    A two-square-inch leaf falling from a tree will be
    instantly accelerated to 20 mph. So will a two-inch cube of
    styrofoam whirled up by a passing truck.

    A massive raindrop presenting two square inches of surface
    area will splatter. So, to a lesser but more disgusting
    extent, will the more plausible dropping from a turkey
    vulture.

    A hovering hummingbird will be badly injured, if not killed
    by your shoulder, while a big piece of gravel tossed in
    front of you by a spectator will leave a bruise.

    The stub of a broken tree branch met dead-on at that speed
    may go all the way through your shoulder and possibly kill
    you.

    A regulation golf ball is 0.168" in diameter and weighs 1.62
    ounces---ouch! I hope that this isn't what led to your
    question, since they're usually moving rapidly.

    Perhaps you could get at whatever you have in mind by
    imagining a 155 pound hammer moving at 20 mph and smacking
    into some small object that you dislike?

    If the object is momentarily free in the air in front of
    you, little force is transferred, despite the pain, the only
    resistance to your stately progress being the negligible
    wind resistance of two square inches, plus the equally
    negligible mass of such a small object when compared to your
    mass. You weigh about 1,530 golf balls.

    Helpfully,

    Carl Fogel
     
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