质点系的动能为 7=∑2m=2 +) ec/ =∑ +y2+21·1 Mv2+∑ 1 2 2 ==Mv+ 其中ΣmV=Mn=07=∑m28 质点系的动能为: 其中  mi vri = Mvrc = 0 2 2 1 i ri T =  m v 2 2 1 i i T =  m v ( ) ( ) i c r i c r i =  m v + v  v + v 2 1 ( ) i c r i c r i =  m v + v + 2v v 2 1 2 2 = + + ( ) c i r i c i r i M v m v v m v 2 2 2 1 2 1 = M vc +T 2 2 1