Axis

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Etymology

Latin, axis, axle; akin to Old English eax axis, axle, Greek axōn, Lithuanian ašis, Sanskrit akṣaḥ

Definitions

  • 1 a : a straight line about which a body or a geometric figure rotates or may be supposed to rotate b : a straight line with respect to which a body or figure is symmetrical —called also axis of symmetry c : a straight line that bisects at right angles a system of parallel chords of a curve and divides the curve into two symmetrical parts d : one of the reference lines of a coordinate system
  • 2 a : the second vertebra of the neck on which the head and first vertebra turn as on a pivot b : any of various central, fundamental, or axial parts
  • 3 : a plant stem

84 : one of several imaginary lines assumed in describing the positions of the planes by which a crystal is bounded and the positions of atoms in the structure of the crystal

  • 5 : a main line of direction, motion, growth, or extension
  • 6 a : an implied line in painting or sculpture through a composition to which elements in the composition are referred b : a line actually drawn and used as the basis of measurements in an architectural or other working drawing
  • 7 : any of three fixed lines of reference in an aircraft that run in the longitudinal, lateral, and vertical directions, are mutually perpendicular, and usually pass through the aircraft's center of gravity
  • 8 : partnership, alliance
  • 9 : a point or continuum on which something centers <an axis of social power>

Description

A rotation is a movement of an object in a circular motion. A two-dimensional object rotates around a center (or point) of rotation. A three-dimensional object rotates around an imaginary line called an axis. If the axis of rotation is within the body, the body is said to rotate upon itself, or spin—which implies relative speed and perhaps free-movement with angular momentum. A circular motion about an external point, e.g. the Earth about the Sun, is called an orbit or more properly an orbital revolution.