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[Chareyre <bruno.chareyre@xxxxxxxxxxx>]

If the normal is b1->b2, it makes more sense to define the force as
"applied by b1on b2". My two cents...

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NormalShearInteraction::{normalForce,shearForce} has undefined orientation
https://bugs.launchpad.net/bugs/493102
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Status in Yet Another Dynamic Engine: Confirmed

Bug description:
NormalShearInteraction::{normalForce,shearForce} should contain forces on the interaction, which can be used for various purposes by other functions. However, different functors use them with different sign

ef2_Spheres_Elastic_ElasticLaw (a.k.a. ElasticContactLaw):

   applyForceAtContactPoint(-currentContactPhysics->normalForce-shearForce, ... )

Law2_Dem3DofGeom_CpmPhys_Cpm:

   applyForceAtContactPoint(BC->normalForce+BC->shearForce, ...)

This is a convention issue, but must be fixed. Should normalForce and shearForce be oriented as it applies on id1 (first case) or id2 (second case)? 2nd case is nicer WRT applyForceAtContactPoint syntax, but that one is arbitrary as well.