Equation 10 Equation 14 Galilean relativity
Equation 10 and Equation 14 can be interpreted as giving the resultant 




u



{\displaystyle \mathbf {u} }

 of the two velocities 




v



{\displaystyle \mathbf {v} }

 and 





u
′


,


{\displaystyle \mathbf {u'} ,}

 and they replace the formula 




u
=

u
′

+
v



{\displaystyle \mathbf {u=u'+v} }

 which is valid in Galilean relativity. Interpreted in such a fashion, they are commonly referred to as the relativistic velocity addition (or composition) formulas, valid for the three axes of S and S′  being aligned with each other (although not necessarily in standard configuration).
