Hello everyone, I am confused with the minus sign of x'=x-vt. When there are 2 references frames called K and K' which K is at rest and K' moves to right with velocity V with respect to K. Let there is another frame which is my frame of reference called O. The vector sum of the displacement should be OK'=OK+vt which equals x'=x+vt. However, this is wrong. So, I want to ask that what is the physical meaning of the minus sign of Galilean Transformation? Besides, can we apply the concept of relative motion to derive the Galilean Transformation?