Rest (physics)

Rest in physics refers to an object being stationary relative to a particular frame of reference or another object. According to the theory of relativity it is said that an object is: at rest relative to another. For example, a train decelerates on approach to a station and eventually stops alongside the platform. The train can be said to be at rest with respect to the station or just at rest, since in practice we do not need to specify the frame of reference if it is obvious from the context.

By Albert Einstein's celebrated definition^{[citation needed]}, two observers measure having been at rest relative to each other in a particular trial if they succeed to identify a third observer as middle between each other.

In fact, there is nothing at absolute rest. For example the earth is rotating around the sun which is rotating around the galaxy and so on.

The concept of relative rest is closely linked to that of inertial observers and the statement that nothing is at absolute rest is loosely equivalent to stating that there are no frames of reference which are truly inertial. So called non inertial observers are is dealt with in the theory of general relativity.