IRockyContact is an interface for the internal contact object in Rocky. A contact object is the code representation of the relationship between two particles or between a particle and a geometry triangle that have a force interaction at a given time. In the first case, it will be a particle-to-particle contact (sometimes abbreviated to particle-contact), whereas in the latter case, it will be a particle-to-triangle contact (sometimes abbreviated to triangle-contact).

A contact in which there exists an actual overlap between the entities is referred to as a frictional contact. If an adhesive model is active, an adhesive force might exist even if the entities are not physically touching each other. In that case, an adhesive contact will be established between those entities.

In a particle-to-particle contact, one of the particles is identified as home particle, whereas the other is identified as near particle. There is no special rule for labeling particles in this type of contacts, any of the two particles can be labeled as home or near. On the other hand, in a particle-to-triangle contact, the particle is always referred to as home particle, while the triangle is referred to as near triangle. Whenever it is necessary to distinguish between two contacting entities, the prefixes home and near are used in the associated method names. The normal unit vector associated to a contact is always constructed pointing to the home particle.

Contact scalars are special variables that store values per contact that are preserved between time iterations. The preservation of those values is guaranteed during the whole lifetime of a contact. Internally, contact scalars are stored separately for particle-to-particle contacts and for particle-to-triangle contacts. In order to differentiate them, the former are named particle contact scalars, whereas the latter are named triangle contact scalars