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Expressed in an abstract manner we may say: If a mass m is moving

uniformly in a straight line with respect to a co-ordinate system

K, then it will also be moving uniformly and in a straight line

relative to a second co-ordinate system K′ provided that the

latter is executing a uniform translatory motion with respect to

K. In accordance with the discussion contained in the preceding

section, it follows that:

If K is a Galileian co-ordinate system. then every other

co-ordinate system K′ is a Galileian one, when, in relation to K,

it is in a condition of uniform motion of translation. Relative

to K′ the mechanical laws of Galilei-Newton hold good exactly as

they do with respect to K.