As I've just recently started studying relativity, I need some help with these basic concepts. So this thread is about length contraction. Can somebody explain the effects of it, since I've already found out some things, like the existence of the invariant proper lenght, the fact that contraction is in the direction of the motion of the object. Is the length of the object the only property that is affected by length contraction? For instance, does its proper mass stay invariant, its composition and so on? Thanks in advance.