Fist off, this isn't homework, so... I'm doing an investigation, calculating gravity, and I have 2 experiments ready, with everything accounted for. However, I do not know some variables for my other 2 experiments. 1. Ball on a Slope. I am rolling a ball on a slope through 2 light gates, and calculating the final velocity and time it took for the ball to pass through. However, I understand how friction would be a factor, and so I tried to derive an equation that combined gravity with friction, but I couldn't get one that worked. Could anybody help? 2. Secondly, I wanted to use a Kater's Pendulum, but I can't find any experiments that I could do using one online, and I have no idea how it works. I was just told by my teacher that it is the most accurate method. Thank you for any help you provide! aragonaut Edit: I am doing an SQA Advanced Higher I am rolling it down a slope, because it is a part of my required investigation; I need to use it as an integral part (The introduction.) I need to have an investigation that isn't very accurate, as to provide something for my discussion section to reflect on. Secondly, I have got a Simple Pendulum and a Compound Pendulum already, and I need a Kater's Pendulum Experiment.