Rörelsemassan

Rörelsemassan, the Swedish term for momentum, refers to a physical quantity that represents the product of an object's mass and its velocity. In classical mechanics it is expressed mathematically as \(p = mv\), where \(p\) denotes momentum, \(m\) the mass, and \(v\) the velocity vector. Because momentum is a vector, it possesses both magnitude and direction.

This quantity is central to the principle of conservation of momentum. In an isolated system, the total vector sum of the momenta of all constituents remains constant in time, provided no external forces act. The conservation law arises from the translational symmetry of space, as formalised by Noether’s theorem. It applies to both linear momentum in one-dimensional motion and to angular momentum for rotational motion.

In practical applications, knowledge of momentum is crucial for analysing collisions, rocket propulsion, fluid dynamics, and many engineering systems. Numerical calculations of momentum changes allow prediction of final velocities in elastic and inelastic collision scenarios. Momentum transfer is often mediated through forces, with impulse—defined as the integral of force over time—equal to the change in momentum.

In relativistic physics, the classical formula is modified; the 4‑momentum combines energy and spatial momentum components. However, the underlying principle of conservation remains valid across all relativistic regimes. Rörelsemassan thus serves as a foundational concept that links kinematics, dynamics, and symmetry principles within the broader study of physics.