# Coefficient of friction between two different materials

Hi I am new to DEM simulations

In FrictMat() we define friction angle for let says a sphere and some different material is assigned for the wall which values does yade take when calculating friction forces between wall and spheres

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Jan Stránský
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 Revision history for this message Jan Stránský (honzik) said on 2021-06-16: #1

Hello,

> I am new to DEM simulations

welcome :-)

> which values does yade take

generally speaking, it may be different for different materials, different contact laws etc.

General "philosophy":
- Material (e.g. FrictMat) stores properties of material = material properties of particle
- IPhys stores properties of interaction = material properties of interaction
- Ip2 defines, how IPhys properties are computed from Material

Note that "material properties of particle" and "material properties of interaction" may be (usually are not, but may be) very different things.
E.g. for FrictMat and FrictPhys:
- FrictMat has frictionAngle property
- FrictPhys has tangensOfFrictionAngle property
- Ip2_FrictMat_FrictMat_FrictPhys has frictAngle property

For the case of FrictMat and Ip2_FrictMat_FrictMat_FrictPhys, by default
Ip2_FrictMat_FrictMat_FrictPhys() # no arguments
takes a minimum value of the two friction angles.

However, you can define a MatchMaker [2] to fit your needs and e.g. take average or maximum value:
Ip2_FrictMat_FrictMat_FrictPhys( frictAngle=MatchMaker(...) )

To get this information, you can:
- build a simple scene (1 sphere, 1 wall, 1 predefined contact) and test yourself

Roughly ordered by preference, but it may differ.
E.g. for beginners, it is ok to ask very basic things here before they learn how to use and search documentation.