Oneaxis

Oneaxis is a term sometimes used to describe systems, models, or objects that are defined by invariance or a reference to a single axis of symmetry. In formal contexts, the concept is more commonly referred to as axial symmetry or one-axis symmetry. The idea centers on having a distinguished axis around which properties remain unchanged or around which a transformation acts single-dimensionally.

In rigid body dynamics, an object with two equal principal moments of inertia (I1 = I2 ≠ I3) is described as axially symmetric or one-axis symmetric. The symmetry axis corresponds to the third principal axis, and the inertia tensor is diagonal with two equal entries. This symmetry simplifies the equations of motion and yields conserved angular momentum components about the symmetry axis, enabling the description of the motion as that of a symmetric top with predictable precession.

Beyond rigid bodies, oneaxis or axial symmetry appears in geometry and physics in contexts such as surfaces of revolution, cylindrical coordinates, and planetary rotation. In computer graphics and robotics, one-axis rotations—rotations about a single fixed axis—are common for simplification and control, such as yaw around a vertical axis or a single-actuator joint providing rotation about one axis.

Note that oneaxis is not a widely standardized term in formal literature; it is often used informally or as a shorthand in branding or software naming. When precision is required, axial symmetry or one-axis symmetry is typically used to describe the concept.

See also: axial symmetry, symmetry, rigid body dynamics, symmetric top, Euler equations, principal moments of inertia.