👉 A joint, in mathematics and physics, refers to a composite object that has its own internal forces acting on it. It is often used to model systems where the external forces acting on the system are not uniform or constant but depend on the position of the system relative to other bodies. The concept of a joint is fundamental in many fields such as mechanics, thermodynamics, and engineering, where it can help describe how objects move and interact with each other. In physics, a joint is usually defined as