Physically accurate friction settings

[MJNorris]

Hi all,

 

I'm trying to create some physically accurate bullet sims using real world values for mass/density and friction, so I've been looking at some engineering tables for friction coefficients:

http://roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm

What I'm confused about is this:

It seems that real world friction is calculated based on the coefficient of friction between two objects, eg wood & wood has a friction coeff of 0.25 - 0.5; wood and concrete 0.62; wood and metal 0.2 - 0.6.

So friction is not a material specific attribute, so if I have 3 houdini objects, one wood, one concrete and one metal, how do I create realistic friction settings for each combination when I can only set a single friction value per object? Is it even possible?

Also, how does Houdini calculate friction coefficient between two objects? Does it multiply the friction values? Or average them?

Any help is much appreciated

Thanks in advance!