Friction

3D friction is quite similar to its 2D counterpart, with the primary difference being the types of contact pairs involved. In 3D, these contact pairs are point-triangle and edge-edge pairs. Consequently, the barycentric coordinates of the closest points are now two-dimensional, represented by the optimal values of $β_{1}$ and $β_{2}$ in the definitions provided in Definition 24.1.1 and Definition 24.1.2.

In practice, this means that while the principles of friction remain the same, the specific calculations adjust to account for the geometry of the contact pairs in 3D space.