testmassa

Testmassa refers to a small, idealized mass used in physics to probe a field or system without significantly altering it. The term is commonly rendered in English as test mass, but in other languages it may appear as a compound noun such as Testmasse in German or massa di prova in Italian. The central assumption is that the test mass is sufficiently light that its own gravitational, electric, or other fields produce negligible back-action on the environment being studied.

In classical mechanics and gravitational theory, a test mass experiences external forces that arise from the field under study while its inertia determines its motion via F = ma. In general relativity, a test mass is treated as a test particle whose worldline approximates a geodesic of spacetime, neglecting back-reaction on the metric. This simplification allows the analysis of fields, orbits, and spacetime curvature without solving the full coupled equations for the field and the source.

Limitations include situations where the mass is not negligible or where the field interacts strongly with the mass, in which case back-reaction must be included and the test-mass approximation breaks down. In quantum settings, the concept is further refined to account for quantum uncertainties and back-action.

See also: test particle, geodesic, back-reaction, principle of equivalence.