masspoint

Masspoint, also written as mass point, is a simplifying concept in classical mechanics used to analyze the motion of systems of particles and rigid bodies connected by constraints. In this approach, each body is replaced by a single particle located at its center of mass with a mass equal to the body's total mass. External forces are applied to these points, and rotational effects and the finite size of bodies are neglected. The motion of the system is described by Newton's laws for the masspoints.

The method reduces complex bodies to point masses, making it easier to solve problems in statics and dynamics where the primary interest is translational motion. It assumes that all interconnections—such as ropes, strings, rods, or joints—impose constraints on the relative motion of the masspoints, while the internal distribution of mass within each body has a negligible effect on the overall motion. Forces such as gravity, normal forces, tension, and friction are incorporated as external forces on the corresponding masspoints.

Equations of motion are written for each masspoint: the sum of external forces equals the mass times acceleration (F = ma). For systems with constraints, constraint equations relate the accelerations of different masspoints. Momentum conservation and energy methods may also be used, especially in idealized or planar problems.

Limitations include the neglect of rotational dynamics and mass distribution within bodies; when rotation or deformation is significant, rigid-body or continuum models are required. Masspoint is commonly used in introductory physics and engineering problems to build intuition before introducing more advanced modeling.