zweikörperige

Zweikörperige is the German adjectival form of zweikörperig, literally meaning "two-bodied" or "two-body." It is used to describe systems or problems that involve two interacting bodies and commonly appears in physics, astronomy, mechanics and related technical contexts as part of compound terms (for example zweikörperiges System or Zweikörperproblem).

In classical mechanics the two-body problem refers to the motion of two point masses that interact via a central force, most frequently gravity or electrostatic attraction. By transforming to center-of-mass and relative coordinates the problem reduces to an equivalent one-body problem with a reduced mass. Under an inverse-square law the motion is integrable and yields conic-section orbits (elliptic, parabolic, hyperbolic), conserved energy and angular momentum, and closed-form solutions known from Keplerian dynamics. Applications include planetary orbits, satellite motion, and binary stars.

In other domains the two-body approximation appears for diatomic molecules, scattering problems, and the quantum-mechanical hydrogen atom, where separation of variables leads to solvable equations using the reduced mass concept. In general relativity the analogous two-body problem is not generally solvable in closed form; approximate methods (post-Newtonian expansions) and numerical relativity are used, notably in modeling compact-object inspirals that produce gravitational waves.

Linguistically, zweikörperige is an inflected adjective and must agree in gender, number and case with the noun it modifies in German. Its use emphasizes the pairwise interaction and the simplifying assumptions of two-body models.