I would probably stick to those figure without using a formula, empirical evidence is always better (the real world). However as an Engineer, I can tell you that everything falls at 9.81 m/s/s. Most people use 10 metres per second per second. 9.81 is a figure from Newton. One Newton (N) is 9.81 Kilogrammes (Kg) incidentally (but try to forget that for now). Effectively we are measuring acceleration. Assuming no air friction. In the first second everthing dropped, travels 9.81 metres. Yet it accelerates at a rate of 9.81 m/s. It travels 9.81m further for every second it drops. So by the tenth second we are travelling at a speed of 9.81m x 10s = 98.1m/s. And have covered a distance of 9.81m x 10s x 10s = 981m. With no drag we would continue to accelerate. However there is always air friction, and this will affect every shape differently. We must therefore calculate a 'drag co-efficient' for the shape that is falling. This calculation is long and involved. You can look it up but I won't bore you any more than I have. Finally, (don't yawn) you need to draw a graph with your acceleration and your drag co-efficient. Where the lines meet will give you a speed which is your terminal velocity. This is the speed at which you stop accelerating Every shape has a different terminal velocity. Go into a head first dive and you can forget about the figures your instructor has given you. I can only hope the figure skydivers use, take this into account. The graph will also show you where and when terminal velocity is reached. Once you know your drag co-efficient you can put it into a formula with your newtonian acceleration, and work out your actual acceleration up to terminal velocity. Oh and by the way you could have picked something easier, even engineers write programs so they don't have to work this stuff out. You might be able to find a free program if you search it.