noun
relative motion
Physics term describing the motion of an object as observed from a particular reference frame, often contrasted with 絶対運動 (absolute motion).
See also: 絶対運動
相対運動を理解するには、基準となる座標系を決める必要がある。
To understand relative motion, you need to define a reference coordinate system.
絶対運動 is absolute motion, independent of any observer, while 相対運動 is motion relative to a chosen reference frame.
Compound of 相対 (relative) and 運動 (motion).