10-6 Rotational Dynamics; Torque and Rotational Inertia(Page: 280-282) N- I Law for rotation(定轴转动定律)(P244) A rotational rigid body can be considered to be constituted by many parts. The ith part has a mass Am external force Fi internal force f; Applying n- I law on△m2 JA F+f=△ Resolving it into directions t and n: :f+f=△m1ait=△m;ra10-6 Rotational Dynamics; Torque and Rotational Inertia (Page:280-282) external force ; Fi  i f  internal force Applying N-II law on mi: Fi f i mi a    + =  z o i r i f  Fi  mi   ˆ : Fi t + f i t = mi ai t = mi ri  A rotational rigid body can be considered to be constituted by many parts. The ith part has a mass mi , Resolving it into directions and :  ˆ n ˆ 1. N-II Law for Rotation (定轴转动定律) (P244)