relative motion
Movement between observers
Relative motion is movement as measured from a particular point of reference rather than in absolute terms.
A passenger sitting still on a train has zero motion relative to the train but considerable motion relative to the ground.
The relative motion between the two spacecraft was just centimeters per second.
All motion is technically relative—there is no fixed point in the universe against which to measure absolute movement.
- parallaxPosition change from different vantages
- line of sightDirect visual path, unobstructed
- velocityDirected rate of motion
- closing speedRelative velocity of convergence
- speed gunMeasures object velocity remotely
kinematics · acceleration · trajectory · Doppler effect · moving target · inertia · observer · reference frame · radar tracking · displacement · coordinate system · centrifugal force · orbit · aberration · sliding · rolling · shifting · vector
- motionvelocity, speed, momentum, acceleration, locomotion
- timesecond, minute, hour, day, seconds
- mechanicsforce, turning, rotation, momentum, velocity
- rotationrotation, spin, axis of rotation, angular momentum, revolutions
- speed termsacceleration, speedometer, momentum, terminal velocity, average speed
- motion perceptionlooming, persistence of vision