# Re: Physics - biking question

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

1. ### [email protected] Guest

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.