# Physic interaction betweem sphere and polyhedra

hello
i know that Ig2_Sphere_Polyhedra_ScGeom can calculate the ig between polyhedra and sphere, if the material of polyhedra is polyhedraMat and sphere is frictMat, the ip between them can be calculate by Ip2_FrictMat_PolyhedraMat_FrictPhys, and then use cundall law, the interaction between polyhedra and sphere can be solved.
Ip2_FrictMat_PolyhedraMat_FrictPhys describe in Polyhedra.cpp is as below:
void Ip2_FrictMat_PolyhedraMat_FrictPhys::go(const shared_ptr<Material>& pp1, const shared_ptr<Material>& pp2, const shared_ptr<Interaction>& interaction){
Ip2_FrictMat_FrictMat_FrictPhys().go(mat1,mat2,interaction);
}

and stiffness culculate in Ip2_FrictMat_FrictMat_FrictPhys() is like that:
Real Kn = 2*Ea*Ra*Eb*Rb/(Ea*Ra+Eb*Rb);
Real Ks = 2*Ea*Ra*Va*Eb*Rb*Vb/(Ea*Ra*Va+Eb*Rb*Vb);

What puzzles me is that polyhedra do not have radius r, then how to calculate normal stiffness between polyhedra and sphere use Ip2_FrictMat_PolyhedraMat_FrictPhys?

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2019-08-17
2019-08-17
 Jan Stránský (honzik) said on 2019-08-17: #1

> What puzzles me is that polyhedra do not have radius r, then how to calculate normal stiffness between polyhedra and sphere

the same way as it does for walls, facets... just considers that the other body has some artificial radius related to the sphere's radius (e.g. equal) [1,2,3]

cheers
Jan