I don't know if anyone knows about this set of online physics textbook, but I downloaded this 12MB PDF onto my computer. I tried to understand the concepts of states, objects, sequence, duration, and time that it mentioned in the very first chapter. However, when it tried to explain these important things to me, a strange software called mathematica was said to be used to create certain pictures and patterns that were supposed to help make those concepts clear. The problem is I don't have such software! I am forced to stop further reading that textbook. Anyone has any idea how to overcome this? Buy that software?