physea said:
I don't understand the difference between moment of inertia, centroid, and radius of gyration as well as when do we consider each.
Unfortunately, even after several prodding, you don't seem to want to show any indication that you have made an effort to understand these things. It appears that you simply want to sit back and be spoonfed.
You simply can't say "I don't understand so-and-so." You need to explain and elaborate WHY and WHERE you stopped understanding the concept. Describe what you already know. In this case, what is the concept of "moment of inertia", "centriod", and "radius of gyration" that you already know? Without knowing what you know, how are we going to be able to build something on top of that? We don't know where the foundation is!
Here's another things that you need to be aware of. Sometime, in the act of trying to write it down and explain as clearly as possible your problem to another person, THAT in itself can trigger something that might help you understand what it is. Many of us who have to teach this material, even with all our academic degrees, often find that we discover something we either didn't realize or wasn't aware of in the process of making our lecture notes or presentations. In trying to convey the material in a clear, systematic, and understandable manner, it is not unusual that we discover some information that we didn't know before.
So stop simply claiming that you don't understand something. You MUST understand SOMETHING, otherwise you won't be in such a class that requires you to deal with these concepts. At the very least, you should be able to find these definitions either in your text/lecture notes (preferable), or online. Then describe up to what point you understood the concept, and where you stop understanding it.
A patient can't simply walk into a doctor's office and claim that he/she "does not feel well", and expect to get an accurate diagnose. Use that analogy here!
Zz.