acceleration: a,ar am t:=∑△m,i×a,+∑△m,i×am since: xam=0f×a,.=ga.sin90°k=7队 t:=∑△m,rp J=∑△m,2z i i i i i ai n m r a m r             since：   0 i in r a   r a ra k r k i i i i i        2   sin 90    2 z i i  m r 2 i i J  m r    J z  acceleration： ai ai ain      