The science involving the study of biological systems from a mechanical perspective. The science that examines the forces acting upon and within a biological structure and the effects produced by such force. The inter-discipline that describes, analyses, and assesses human movement. Biomechanics: branch of physiology that utilizes the methods of a branch of physics called mechanics to describe, analyze, and asses the effects of internal and external forces on biological structures. Mechanics: branch of physics that analyses the actions of forces on particles and mechanical systems. Classical: describes the relationship between the motion of a body and the forces acting on it: newtonian: laws of motion at low speeds, relativistic: laws of motion at low speeds and speeds near speed of light. Quantum: describes physical phenomena at the atomic level. Deformable body: describes the relationship between the motion of a deformable body and the forces acting on it: all real bodies are deformable to some extent.