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Re: momentum



John Trammell writes:

<quote>
"Velocity" doesn't break bones.
"Acceleration" doesn't break bones.
"Force" doesn't break bones.
The fact that sufficiently DIFFERENT forces are acting on
DIFFERENT parts of the SAME bone causes it to break.
<end quote>

Come on, John. That's just semantics. You've said the same thing I
said, forces break bones. You just used more words than I did. I
considered talking about differences between forces and pressures...
i.e. over what area is the force spread out, and where the forces are
applied, etc., but I assumed people would get the point.

Come on people. The whole point of seat belts, padded dashboards, air
bags etc. is to reduce large forces on various parts of the body.
These kinds of problems are delta-p = intregral(Fdt) problems. Spread
that delta-p over long time (and also spread the resulting force over
large areas) to keep the differential forces on any body part below the
breaking point or injury point.

By the way, if I jump out of an airplane I don't have a force of one
'gee' on me. I have a force equal to my weight = mg on me. But I
don't have to jump out of an airplane to get that. I also have that
force on me as I sit here and type this. Also, as I sit here, I have
the additional force of my chair pushing up on me. Geez, my pelvis and
the bottoms of my thighs are being squeezed between my weight and my
chair, but no broken bones. Of course not, our bodies are designed for
that. But ram my head into the windshield at 55 mph... my skull is not
designed for that kind of force.

Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817