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# Frame of reference definition

A frame of reference is a coordinate system used to measure the physical properties (e.g. position, velocity, momentum) of objects. In physics, the origin of the coordinate system is often the position of an observer.

As there is no known centre of the universe, there is no "correct" frame of reference. The appropriate frame of reference depends on the situation.

A moving object is considered to be stationary in a frame of reference which moves with the same velocity as the object.

A car is moving in the frame of reference of a person standing on the street (i.e. the "perspective" of the person on the street). A person in the car will see the person standing on the street as moving (i.e. the "perspective" of the person in the car).

$v_{1}$. The speed of car 1 in frame S is $v_{1}$ in S but zero in frame S'." src="https://www.toktol.com//Content/images/transparent.gif" onload="conditionalLoadImage(this, 'https://toktolweb.blob.core.windows.net/courseimages/', 'Physics.AL.Dyn.03.png', false, {}, 'https://toktolwebcdn.blob.core.windows.net/quizimages/')" name="Physics.AL.Dyn.03.png" sub="A stationary reference frame S and a moving reference frame S' with a speed $v_{1}$. The speed of car 1 in frame S is $v_{1}$ in S but zero in frame S'." />
A stationary reference frame S and a moving reference frame S' with a speed $v_{1}$. The speed of car 1 in frame S is $v_{1}$ in S but zero in frame S'.