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Re: The Olympics



John Barrer's egg drop project undoubtedly rotates because of air
resistance. A significant couple results from the fact that a structure
like the one he describes has the force of gravity acting at the centre of
mass, somewhere in the egg, significantly displaced from the "centre of air
resistance" on the whole structure. Sky divers exploit this effect by
arching their back and sticking out their limbs in order to fall belly-down.

Mark


At 04:42 02/10/00 , Doug Craigen wrote:
John Barrer wrote:
>
> Doug - I see your point, BUT if that's so, then "how
> come" an egg drop project that is top-heavy will
> rapidly tumble on its way to the floor. I have seen
> many toothpick projects with the egg perched on top of
> an elaborate energy-absorbing structure quickly rotate
> in free fall so that the egg lands first! John Barrere

I don't know what experiment you are refering to, but in my experience
being top-heavy does not cause a falling object to rotate. As a quick
test before risking putting my foot in it yet again... I went to me tool
box and took a variety of top heavy objects such as hammers and dropped
them from a few different angles of inclination, and in all cases they
hit the floor at the same angle of inclination as I had dropped them
from. (reading that last sentence I'm a bit worried since there is a
grammar analysis going on in another thread, but I'm too tired to go
back and rework it right now, I'll just take any flames that come ;-)).

I think the free-body question is a good basic one, its what I always
tell my students to do so why not myself or a colleague? Having thought
about it a bit now I can see all kinds of dynamic ways of achieving zero
angular momentum rotations, but I cannot see any way of constructing a
free body diagram demonstrating that a static shape begin rotating due
to gravity alone.

\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\_/^\

Doug Craigen
http://www.dctech.com/physics/about_dc.html


Mark Sylvester
United World College of the Adriatic
Duino TS Italy
+39 040 3739 255