peteroznewman
Subscriber
If you pick the wrong shell face, frictional contact will not work. I don't think penetration tolerance has anything to do with the issue. You imagine that once the shell has passed through the solid surface, it will now be looking at the target face. I don't think it will. You can do an experiment and see what happens.
Think of the red and blue faces of the frictional contact pair as mirrors with a red or blue sticker on the mirror side. If the mirrors are facing each other, each sticker can see the other. If you flip one mirror (change Top to Bottom for example), now both mirror cannot see the other sticker. If you move the flipped mirror to the opposite side of the mirror on the solid, penetrating the solid, the shell mirror can only see the back side of the solid mirror. Both mirrors still can't see the other sticker.
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