John Jensen on mon 30 apr 01
I don't believe in centrifugal force. At least not in the context of wha=
t
might be called uniform circular motion, such as what is involved on the
pottery wheel. It is convenient to call that tendency of things to fly o=
ff
the wheel centrifugal force, but in fact there is no vector of force whic=
h
is oriented outward from the center. There is a force along the tangent =
to
the circle. There is a force (applied by the hands, for example) toward =
the
center which we might call a centripetal force. The balance of these two
forces creates uniform circular motion. If a ball were placed exactly in
the center of the wheel, it would not move outward...there is no outward
force. If a ball were placed at some other point on the wheel, it would
accelerated along the tangent of the circle which includes the point of
contact.
So even though it is inconvenient to do so I try to refrain from decribin=
g
any effect in pottery as being due to a centrifugal force.
John Jensen, Mudgbug Pottery Annapolis, Md. mudbug@toad.net
www.Toadhouse.com
Martin Howard on tue 1 may 01
John Jensen is correct of course, but all movements which we normally
describe as centrifugal are the same. The object, liquid, whatever, is go=
ing
off at a tangent, just like so many of us on Clayart :-)
But I think centrifugal is generally understood and it does mean a fleein=
g
=66rom the centre. It does not imply a direct fleeing from the centre.
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
Snail Scott on tue 1 may 01
At 03:55 PM 4/30/01 -0400, you wrote:
>I don't believe in centrifugal force. in fact there is no vector of for=
ce
which
>is oriented outward from the center. There is a force along the tangent=
to
>the circle. There is a force we might call a centripetal force. ...the=
re
is no outward
>force. If a ball were placed at some other point on the wheel, it would
>accelerated along the tangent of the circle which includes the point of
>contact.
>John Jensen
Strictly speaking, this is true. On the other hand,
since that tangent force IS acting on the work, and
since the larger the diameter becomes, the greater
the velocity at that perimeter point, that force will
tend to cause the clay to move outward. Since the clay's
location is constrained by its attachment to the clay
around it, the effective result is that the rim of tall
wide bowls will tend to expand outward. 'Centrifugal
force' may not be a term physicists acknowledge, but we
may as well call it something, hmm?
-Snail
p.s. My resident physicist isn't here to read this, so
you're only imagining the tooth-grinding noises which
would normally accompany any such statements as the
one above! ;)
craig clark on tue 1 may 01
I like the general description of centrifugal force as a fleeing from
center. I flee from center all the time and it's nice to know that I can
blame it on some force. The tangent thing also strikes to home.
I flew off (due to unseen cetrifugal forces) into a tangentely heated
debate with my mother-in-law, who I dearly love, about SUV's. I think
they're a menace. She doesn't. Acussed me of being intolerant. I was.
Anyway, I'm slowly calming and regaining center. Time to set my butt
down at the wheel.
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
-----Original Message-----
From: Martin Howard
To: CLAYART@LSV.CERAMICS.ORG
Date: Tuesday, May 01, 2001 7:58 AM
Subject: centrifugal force?
>John Jensen is correct of course, but all movements which we normally
>describe as centrifugal are the same. The object, liquid, whatever, is
going
>off at a tangent, just like so many of us on Clayart :-)
>But I think centrifugal is generally understood and it does mean a fleei=
ng
>from the centre. It does not imply a direct fleeing from the centre.
>
>Martin Howard
>Webb's Cottage Pottery
>Woolpits Road, Great Saling
>BRAINTREE, Essex CM7 5DZ
>England
>
>martin@webbscottage.co.uk
>http://www.webbscottage.co.uk
>
>________________________________________________________________________=
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melpots@pclink.com.
>
Mike Gordon on tue 1 may 01
John Jensen,
Have you ever been to a street fair where the kids got to put paint on
an electric wheel head with some paper or card stock on it and let it
spin? If memory serves me correctly the paint spread out in all
directions. What kind of "force" could that be???? Mike Gordon
Philip Poburka on wed 9 may 01
Dear Craig,
enjoyed your post!
My understanding of Women would affirm, that they are likely to instruct
very capably, if sometimes obliquely, in matters of 'unseen centrifugal (AND
centripedal) forces', and sweetly enough at that, if we are wise to enter
into 'arguments' with them, only with that in mind.
I still have a shallow 'dent' just above my temple...from a
'hand-bag'...(years ago) which was accelerated quite smartly, in an 'arc',
to communicate some 'point' or other, in the address of some 'science'
argument ...
I did see 'stars' for a little while...but no 'birdies' tweeting 'Brahms
Lullabye'...
Or only in the anticipation, that we may not wish to get on the 'wrong'
side
OF these 'forces'...
The para-centrifical Force of 'pride' for example, being if Scientifically
elusive, none-the-less plenty able to effect remarkable reconfigurations in
the rhelms temporal and other, and to 'accelerate' matters with
devil-may-care regard to 'G' forces, inertia or respect for the Laws of
Thermo-dynamics or Gravity.
Matters which I suppose only lately, have 'Physicists' found the methods to
investigate, and ponder.
"Hell hath no Fury..." - indeed!
Phil
l v nev
> I like the general description of centrifugal force as a fleeing from
> center. I flee from center all the time and it's nice to know that I can
> blame it on some force. The tangent thing also strikes to home.
> I flew off (due to unseen cetrifugal forces) into a tangentely heated
> debate with my mother-in-law, who I dearly love, about SUV's. I think
> they're a menace. She doesn't. Acussed me of being intolerant. I was.
> Anyway, I'm slowly calming and regaining center. Time to set my butt
> down at the wheel.
> Craig Dunn Clark
> 619 East 11 1/2 st
> Houston, Texas 77008
> (713)861-2083
> mudman@hal-pc.org
Michael McDowell on fri 11 may 01
This discussion has gone on for quite a long time (and I've hardly read a=
ll
the posts on the subject), yet I've not noticed a definitive post on the
subject thus far. To my understanding, a physicist, of which we have more=
than
one on the list, should be able to describe how the apparent action of
"centrifugal force" is actually a combination of physical forces. "Centri=
fugal
Force" is aptly called a "pseudo-force" because it is actually a combinat=
ion
of the force of angular momentum and the forces exerted through a fulcrum=
(in
our case, the center of a wheel) causing angular momentum to change momen=
t by
moment as the wheel spins. As long as a piece of clay or slip is bound to=
all
these forces it behaves as if under the action of "centrifugal force". Th=
at is
why it radiates in a more or less straight path out from the center as lo=
ng as
it is bound by the wheel head. But it is also true that as soon as it bre=
aks
free of the fulcrum it will fly off in the direction of just the angular
momentum imparted at the moment it breaks free of the fulcrum.
One can easily demonstrate these facts to oneself by simply dribbling wat=
er or
thin slip near the center of a dry wheel head. As long as the drops are
attached to the wheel they will follow a mostly straight path outward.
Actually, the drag of wind resistance pushes the drops slightly off strai=
ght
in the opposite direction of wheel rotation. However, if one watches the
direction of the drops as they leave the wheel surface, they will be seen=
to
fly off in the same direction they were headed when they break free of th=
e
wheel. For us wheel potters, the combination of forces is constant as lon=
g as
a piece is firmly attached to the wheel, and we may appropriately regard
"centrifugal force" as real. But when we break free of the wheel (As when
splashing oxide from a brush onto a pot) we'd be advised to keep these fo=
rces
separate in our minds lest we miss the pot altogether.
Michael McDowell
Whatcom County, WA USA
michael@mcdowellpottery.com
http://www.mcdowellpottery.com
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