No Yo Yo

Don Rosa donrosa at iglou.com
Tue Mar 23 14:02:14 CET 2004


By the way... and I don't want to get out my old college physics and
thermodynamics and mechanics of deformable solids textbooks... or my old
slide rule... (actually, it might be fun to get out the old slide rule and
show it to a twenty-something engineering student and try to convince him
what it is and what we did before pocket calculators... he'd split a
gut)(then I could put it on eBay!)...
But all this talk about a yo-yo effect of a Duck falling through the center
of the earth seems to be ignoring something very important... actually LOTS
of very important things, those being vectors of force in an infinite number
of directions other than straight up and straight down. You're all thinking
very one-dimensionally. Forget the idea of how this would need to be done in
a vacuum due to air friction (I dealt with a falling body pulled by gravity
into the atmosphere in "The Duck Who Fell to Earth"), forget about air
pressure, forget everything else...
What about the fact that a body at or anywhere near the earth's core is NOT
only being pulled straight toward the exact center of the earth until it
crosses that precise point. It's also being pulled UP as more and more of
the earth's mass is above it. But get this -- it's also being pulled equally
hard in ALL directions to the right, left, front, back, etc., etc. I should
think that all of these forces would be like puttin' the *brakes* on the
falling Duck (or whatever), and there would likely be no yo-yo effect at
all... the Duck would fall slower and slower and finally just drift very
slowly to the center of the earth's gravitational mass, being pulled in
every possible direction. That's why a Duck at the earth's core would be
weightless... NOT because it's being pulled equally up and down... but
because it's being pulled every whichaway. (Sorry to show off and use my old
engineering terms like "every whichaway" on you laymen, but I am, after all,
a civil engineer in my former life.)





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