Hi guys. Ok I'm working on this problem, it's more theoretical than anything.:yuck: I'll try to explain as best I can. Lets say you have a runner going past the following points up till and past 30 m: Distance (x) of x1=0, x2=4, x3=9, x4=20, and x5=30m the times to these intervals are 0, 1.0s, 2.0s, 3.0s and 5.0s. Now if all I did to find velocity was V=d/t, this would only give me an average velocity over that time. Now if I wanted to find the velocity right at that time point, I was told to use the central difference method: V at time 3.0s = (Distance at x4- distance at x2)/(time from distance x2 to distance x4) This should give me the velocity at that point? Now the BIG question is? how am I suppose to do it for those values at the end and at the beginning, ie. when time is 5.0 secs? Thanks guys.