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# friction models

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Hi, just wondering if anyone can explain/point me to some webpages, to explain some of the friction measurements used in some physics engines. Some engines, like dynamechs and newton use two values: static and kinetic friction. I remember these from school, f=kN, where static is the coefficient before the object is moving, and kinetic once the object has started moving. However ODE, uses a "coulomb friction coefficient" and I''m not really sure what this means, and how it relates to static&kinetic friction - is there a way to convert between the two systems? also, tokamak uses "friction" does anyone know what exactly that is meant to mean? Newton also has a ''softness'' force, is this just a fudge factor? Likewise for restitution, tokamak and Newton have this coefficient, but ODE just has a ''bounce'' force - what exactly is that? And dynamechs has a spring and dampner based system for ''bounces'' -- would there be any way to relate these coefficients to the coefficient for restitution? Thanks.

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Here's an article that I highly recommend on the subject, by Jeff Lander. You'll have to register at gamasutra.com (free) if you are not already registered.

The Trials and Tribulations of Tribology

(Tribology = science of friction)

Graham Rhodes
Principal Scientist
Applied Research Associates, Inc.

[edited by - grhodes_at_work on June 5, 2004 1:23:28 AM]

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Thanks for that link. That was a great article.
So far, from my searching around, as far as I can tell all the friction systems are the same. However, some physics engines, such as ODE, and tokamak, only model static friction.

I am still unsure about the physical equivalents of various ''softness'' forces, and am still unsure about ODE''s bounce and dynamechs springs. If anyone has any further information that would be greatly appreciated.

(incidentaly, you can also get the article, in PDF format (without needing to register with gamasutra) here:

The Trials and Tribulations of Tribology

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I thought that what you mentioned in the first post was the Coulomb model of friction.

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