Re: The real effect of centrifugal force
From: TimR (timothy42b_at_aol.com)
Date: 07/23/04
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Date: 23 Jul 2004 00:01:20 -0700
briggs@encompasserve.org wrote in message news:<LymZPCnuAA4f@eisner.encompasserve.org>...
> In article <a88af92f.0407200146.5242f9a4@posting.google.com>, dwb1729@yahoo.com (David Bandel) writes:
> > dcshead@charter.net (Donald G. Shead) wrote in message news:<48402bae.0407191841.4715def1@posting.google.com>...
> >> Centrifugal force is mistakenly thought to cause a body to fly out of
> >> its circular path; along a tangent direction which represents the
> >> inertial path of Newtons inertial motion.
> >>
> >> Actually centrifugal force, when not restrained as by a string or
> >> sling causes a body to flee the center of an evolute radially; along
> >> involutes that remain directed radially away from the center:
> >>
> >> Like the sling used by David to slay Goliath; when it is released the
> >> missile travels radially away from the center to points equidistant
> >> along the tangent.; at potentially lethal speeds depending on the
> >> speed it has when it is released from the evolute.
> >>
> >> There is nothing fictitious about centrifugal force!
> >
> > not true. you're mistaking the difference between letting go of the
> > other end of the string and the string vanishing completely. if u let
> > go of the string sure it'll fly off radially.
>
> No. It'll fly off tangentially.
>
> Or, to be perfectly accurate, it'll fly off _both_ radially and
> tangentially.
>
> If you stay with the rotating frame, looking down your arm at the
> sling stone, it'll appear to fly off radially. At least until
> Coriolis rears its head and the stone veers off anti-spinward.
> (Ever played catch on a merry-go-round? Amazingly difficult.)
>
> If you work from an inertial frame, standing behind the slinger
> and watching the stone, it'll appear to fly off tangentially.
>
> Both descriptions work and both descriptions wind up with the stone
> impacting Goliath's head at the same relative speed.
>
<snip>
Not true. If you do it this way your stone drops limply to the ground
about halfway to Goliath's head.
It is probably better to stay with the inertial frame in this case,
because the sling projectile's velocity after release is not simply
the linear speed during rotation.
During the release interval, most of the speed is generated by moving
the center of rotation a large distance forward. Therefore your
rotating frame becomes much more complicated than your inertial frame.
The assumption that the sling whirls around a stationary center and
the speed is the radius times the angular velocity is as bogus as the
assumed spherical horse in the old joke. MOST of the sling effect
comes from moving the center (all of it if you include the fact that
small linear motions of the center cause the whirling). That should
change your picture of the direction the mass travels as well.
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