Im stuck with an IB extended essay I dont understand at all. Im investigating the relationship between the mass of two soccer balls and the rebound height the top ball reaches when both balls fall from a fixed height. My way of adding mass to the balls is pretty crude, some tape and some weights. What kind of errors am i looking at ? Im also noticing a very uneven relationship between restitution and the mass added. Does arrangement of the added masses have anything at all to do with the rebound height? Does sticking tape alter the balls compression? Can it alter spin ? How does spin affect the rebound height? Please do try answering some of my questions! Ill be really grateful.