What do a proper vector class need? (physics vector)

Hello. I have realized that I need to make a good vector class for my games, it's 2d, I found this game and got really interestaded in making something physics driven, like an application were you can drop a ball in a level and the ball follows the level, for starters. One problem in the vector class I made before this showed itself when I wanted to make all movement time based. How do you do it? And how du you split a vector in two, do you use two temp valiables and use the values once? Well, thanks for all replies!