To be used when the question involves contact forces acting on one/many body systems and accompanying dynamical changes. For general questions,use [mechanics] and for contact mechanics based questions,use [contact-mechanics]
Contact mechanics can be defined as the study of bodies under dynamical deformation and stresses when subject to dynamical forces on contact. It is a specification of classical mechanics to bodies in contact or those in periodic contact and has many applications especially in engineering and other physical-activity based work.
How and when to use this tag
Use the contact-mechanics tag if the question pertains bodies acted upon by dynamical forces which result in deformative and stressful actions on the surface of the body. The more general classical-physics tag may also be used in posts where the contact is periodic i.e when there are certain moments of contact between bodies followed by periods of non contact. Much more general terms such as hamiltonian-formalism or lagrangian-formalism can be used if related quantities such as the Lagrangian ($\mathcal{L}$) or Hamiltonian of the system ($\mathcal{H}$) are present/used. In general the question must specify if the problem at hand is related to other mechanics sub-branches.
Further information
If there are no forces involved, statics and kinematics can also be used. More generally a good tag would be dynamics (dynamics). If the bodies are fluidic in nature, then fluid-dynamics could also be used. The tag can also be used in case the situation involved include solid-fluid interactions at the classical level. forces can in principle also be used but is generally not. Incase of elastic or inelastic collisions between bodies (especially liquids),then the tag elasticity or such could also be used.
Further reading
Handbook of Contact Mechanics by Valentin Popov, Markus Heß, Emmanuel Willert,2019
Contact Mechanics by L.K Johnson,2012
Contact Mechanics and Friction,V.Popov,2010.
