# Re: [ARSCLIST] Mostly for laughs

```--- "Steven C. Barr(x)" <stevenc@xxxxxxxxxxxxxx> wrote:

> I suspect that this may not be entirely correct. The phenomenon we
> refer to as "centrifugal force" is actually the straight-line
> inertia
> of an object moving in a circular path (or a portion of one). For
> this reason, an object placed on the surface of a rotating
> phonorecord
> will fly rapidly outward...and it would seem that the stylus would
> similarly try to do so, but be prevented in doing so by the
> outside wall of the groove. After all, if you were to place the
> tonearm on an ungrooved disc, would it not fly outward>

What causes it to move outward is the fact that the axis of
rotation under the stylus is not perpendicular to the tonearm
pivot point.  With a typical angled or curved tonearm, the
stylus contacts the record at a point below 90 degrees in
relation of the spindle to the pivot point. Therefore, the
surface of the blank record is not moving "south" as observed
from the cartridge, but "southeast" and therefore it tends to
push the tonearm in an "easterly" direction.  Now, an object
placed on the surface of the record, which rotates with
the record, will be subject to centrifugal force because
*it is rotating*.  But, neither centrifugal not centripital
force are acting on the tonearm because the tonearm isn't
rotating.  Centrifugal force isn't a "real" force like
electromagnetism that can be transferred from one body
to another, it's an effect of the Newtonian law of
physics that any moving body wants to continue moving
in the same direction.  Since any point on a rotating
body is constantly changing direction, it "wants to"
move away from the axis of rotation in a the direction
that it's heading at any goven point.  That direction,
however, is not *radial* to the axis of rotation, but
in the direction of the axis of rotation.  Take a look
at water flying off a rotating tire.  It doesn't fly out
radially, it flies out in the direction of rotation.

David Breneman         david_breneman@xxxxxxxxx

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