Because the coefficient of friction depends on the surface
If a ship will be sailing through warm and cold water, people think about making it less dense than the warmest water as they load the ship with cargo. I think you forgot to give the options along with the question. I hope that this is the answer that has actually come to your desired help.
Color Basics
Three Primary Colors (Ps): Red, Yellow, Blue.
Three Secondary Colors (S'): Orange, Green, Violet