1. The problem statement, all variables and given/known data In a water pipe, the light moves in the same direction of the water flow. It is determined that the speed of light is dependent on the speed of water flow. Does that violate the principle of relativity? 2. Relevant equations 3. The attempt at a solution why the speed of light is dependent? I know it should not be violate the principle of relativity but I don't know how to explain.