lecture 3

types of force:

1. parallel force
2. cross force--add verticals

others could divide into these two types

matrix types

F_R M_o ==0?

1. n|n| force&couple
2. y|n| couple
3. n|y| force
4. y|y| balance force

how to calculate F_R and M_O of a force system? use formula? graphical method?