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naborghese48
11-08-2007, 02:18 AM
Dear all,

I am really sorry for my spelling error which made my message at
least unclear. I have written momentum instead of (and meaning
moment), sorry for this. So the correct message would be the following.

I find a subtle difference between torque and moment of a force.

From my remembering of physics books, moment of a force (with
respect to a point or to an axis) is proportional (through the
inertia) to the rotational acceleration. That is it induces a change
in rotation of the body. In this respect we can also represent the
effect of the moment (of a force) as a torque which is a vector
oriented as the rotation axis and has magnitude equal to that of the
moment (of the force).

From my point of view torque can be considered an abstract
equivalent representation of the moment (of the force), that is the
same torque can be generated by a shorter arm and a larger force or viceversa.

From the biomechanics point of view, when analyzing a body joint
from a global point of view we may talk as (net) torque on the
articulartion, but if we want to talk at a more detailed level I
would prefer to read about the moment of the different muscles (which
is implictly due to stretching visco-elastic force plus the offset
between insertion point and point of istantaneous rotation).

Just the same as the difference between 'jam' and 'marmelade'

Cheers

Alberto Borghese

At 15.18 08/11/2007, Adrian Smith wrote:

>www.oed.com
>
>The Oxford English Dictionary has TORQUE (noun):
>
>"The twisting or rotary force in a piece of mechanism (as a measurable
>quantity);
>"the moment of a system of forces producing rotation."
>
>Leeds University Library
>+44 (0)113 3435531
>
>
>-----Original Message-----
>From: * Biomechanics and Movement Science listserver
>[mailto:BIOMCH-L@NIC.SURFNET.NL] On Behalf Of Altinus L Hof
>Sent: 08 November 2007 09:41
>To: BIOMCH-L@NIC.SURFNET.NL
>Subject: Re: [BIOMCH-L] Torque or moment about a joint
>
>Dear All,
>That is an interesting discussion, indeed, about possible differences
>between moment and torque.
>To a great extent this is a 'jam or marmelade' discussion. It just
>happens that English has two words for (about?) the same thing.
>I have the privilege to teach biomechanics in the Dutch language, and
>Dutch has the word and concept 'moment' but no equivalent of 'torque'.
>For all I know it is similar in German (and other languages?). The
>problem is then, when students are to write something on mechanics in
>English, they ask which of the two terms to use. My answer is: the
>meaning of both words is the same, but you better use 'moment'.
>
>In English or US textbooks as a rule one of either term is used, and it
>is stated that both terms are equivalent. A quick scan of my bookshelf
>showed that 'torque' is used by
>- Hamill & Knutzen
>- Kreighbaum & Barthels
>- Mc Ginnis
>And 'moment' by
>- Winter
>- Tozeren
>- Robertson ('Introduction..')
>- Robertson et al. ('Research methods..')mostly
>- Chaffin & Andersson
>- Hibbeler (engineering text)
>- Prentis (,,)
>- Zatsiorsky (Kinetics of human motion)
>
>The latter reference, for me in difficult cases the ultimate authority,
>suggests to reserve the term 'torque' for the moment of a couple ( p.
>19).
>The special thing of such a moment is, that it is a free moment and does
>not depend on the location of the axis with respect to which it is
>calculated, different from the moment of a single force.
>In the example of Young-Ho Kwon: with a screwdriver you apply a torque,
>with a spanner you apply a moment to the screw or bolt. In biomechanics
>therefore, in my opinion 'moment' is in 99% of the cases the correct
>term, and no major misunderstanding will result if it is used in the
>remaining 1%.
>
>At Hof
>Center for Human Movement Sciences
>University of Groningen
>PO Box 196
>The Netherlands
>
>tel. (31) 50 363 2645
>fax (31) 50 363 3150
>e-mail a.l.hof@med.umcg.nl
>
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Prof. Ing. Alberto Borghese
Department of Computer Science - University of Milano
Via Comelico, 39 - 20135 Milano, Italy
Telephone: +39-02-503.16325 Fax: +39-02-503.16373.
Email: borghese@dsi.unimi.it Skype: borgheseA

Laboratory of Applied Intelligent Systems (AIS Lab)
Via Celoria 20, Edificio CTU-9, http://ais-lab.dsi.unimi.it/
Telephone: +39.02-503.14011 Fax: +39-02-503.14012.
Mobile: +39-349-262.11.92.
Prof. Ing. Alberto Borghese
Department of Computer Science - University of Milano
Via Comelico, 39 - 20135 Milano, Italy
Telephone: +39-02-503.16325 Fax: +39-02-503.16373.
Email: borghese@dsi.unimi.it Skype: borgheseA

Laboratory of Applied Intelligent Systems (AIS Lab)
Via Celoria 20, Edificio CTU-9, http://ais-lab.dsi.unimi.it/
Telephone: +39.02-503.14011 Fax: +39-02-503.14012.
Mobile: +39-349-262.11.92.