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Centrifugal FIELDS, not "forces"



On Wed, 1 May 1996, Alex. F. Burr wrote:

Quote from the latest issue of Science page 485(26 Ap 96)
-
"Any rubble pile rotating at a speed faster than this cutoff would be
torn apart by centrifugal force"
...

torn apart by radial pseudo-fields?


One concept I don't recall seeing in this thread:

Centrifugal force doesn't exist, for the same reason that fields of
electrostatic force, magnetic force and gravitational force do not
exist. The key here is "fields." An e-field is not an "invisible
force," any more than gravity is. (Well, GR issues aside, and Newtonian
gravity concepts.) Without a material object to act against, a field is
not a force or a "field of force," a field is a field. Forces are not
measured in, for example, volts per meter.

So, to keep things clear in my head, I always translate arguments about
"centrifugal force" into actually being arguments about "centrifugal
fields." When an object rotates, does it create an invisible field which
can cause radially directed forces to arise upon objects? Of course not.
But I suspect that much of the public believes this to be the case.

Also, whatever happened to Newton's Third Law? Forces exist in pairs,
there is no "centrifugal" or "centripetal" force. If I lay against the
inner wall of one of those giant amusement park centrifuge rides, there
most definitely is a radially-directed force pair between my body and the
wall. I suppose I could be intentionally confusing, and say that the one
end of the force-pair is the "centrifugal," while the other end is the
"centripetal." But if I should leap over the edge of the ride and be
hurled outwards, both forces vanish and I then can safely say that
"centrifugal force" doesn't exist.

Here's a little demo which can aid in unclogging the audience's conceptual
rigidity over "coriolus" and "centrifugal" pseudo-field concepts.

Obtain a CCD camera and monitor, a large box and a small board. Attach
the board to the camera and tape the box to the far end, so the camera
views only the inside of the box. The board needs only to be long enough
so that the camera views the entire interior of the box, but doesn't view
any of the outside world. Aim a floodlight into the box if needed.

___________
__ camera |
|__|[ | Box
==============================___________|

Scatter some small objects in the box, view the camera's image on the
monitor, then... grab the whole assembly and twist and shake it violently!
Really wail on the thing, toss it into the air and catch it, rotate it on
axis repeatedly, hold the camera end and trace parabolic trajectories with
the box, bash the box on walls and furniture.

For some reason, the video view of the crazily gyrating objects in the box
is *absolutely hilarious.* You gotta try this! The first time I put it
together I had to sit down in between sessions, from the strain of
laughing so hard.

Judicious application of parabolic motions generate momentary
"weightlessness" in a 1-G field, which can lead to very interesting
debates among non-physics passersby, and the crazily swerving objects all
move in obedience to the invisible, nonexistant pseudo-fields caused by
the accelerated frame.

This device started life as an "antigravity generator" museum exhibit
prototype. I was intending to build a small airliner cabin full of
Barbies, GI Joes, and luggage, or maybe a moving-van interior full of
scale model furniture (U-Haul Nightmare Scene!), but the demands of other
projects prevailed.

......................uuuu / oo \ uuuu........,.............................
William Beaty voice:206-781-3320 bbs:206-789-0775 cserv:71241,3623
EE/Programmer/Science exhibit designer http://www.eskimo.com/~billb/
Seattle, WA 98117 billb@eskimo.com SCIENCE HOBBYIST web page