Frame of Reference
A coordinate system along with a clock used to record positions, velocities, and times of physical events.
SI unit
N/A
In depth
Frames are categorized as inertial (non-accelerating, where Newton's laws hold directly) or non-inertial (accelerating/rotating, requiring fictitious forces like Coriolis or centrifugal forces). Motion is relative to the chosen frame.
Examples in the real world
A passenger sitting inside a moving train is at rest relative to the train frame, but moving at 100 km/h relative to the station platform frame.