I guess I'll introduce myself as well: My name is, well, my username, but you can call me Drew (most people do). I'm 18 (a senior in highschool) and in an AP Physics II class focusing on mechanics. I posted something in the advanced physics forum that should probably have been moved here, so I think I'm going to post my questions about rotational dynamics here from now on. If you want to look at my other thread to understand my "problems", please do so: https://www.physicsforums.com/showthread.php?t=114597" Essentially, I have a horrible "text book" (Schaums Outline of Physics for Engineering and Science) that I can't trust, and I have a test on Tuesday. Also, I'm on a break right now and don't have access to the teacher to ask questions. Most of my questions will be focusing on understanding "why" rather than looking for numerical answers. The reason for this is that although I seem to be able to do problems confined to one part of Rotational Dynamics, I cannot seem to integrate all of these "tools" and use them to answer more complicated problems. This is why I think "Why" would help. So if you're sympathetic with my cause, I would appreciate your help. My first question is located in the link; here's another: There are a mix of capitalized letters and lower case letters that confuse the hell out of me. i.e. (M) vs. (m) or (R) vs. (r) Sometimes (M) stands for the mass of the entire system and sometimes it just stands for the mass of the object affected by torque. Is there any standard for this or does it vary from different types of teaching? With (r) & (R), (R) seems to stand for the total radius of the object, while (r) I'm told is the radius of the "torque disc". Take a roll of tape, for example; (r) is the measurement from the center to the edge of the inside circle and (R) is the measurement from the center to the outside of the tape. But isn't the whole system affected by torque? What exactly is a "torque disc"? Another question: How can I find the moment of inertia of an object without using calculus? Is this possible, or am I just supposed to memorize formulas for common shapes? Thanks in advance for my petty questions. I used to be excellent at this stuff, but I fell off a cliff last summer and have lost a lot of my processing ability (no joke). It takes me hours to grasp things that I could have in my sleep before. Ugh.