k m Summary: 02m If the body is subject to: 平衡位置 Fig.15-1 A restoring force that is proportional to the displacement but opposite in sign(F=-kx)i or The acceleration is proportional to its displacement and of opposite sign( a==0x)i or The motion equation is x=Acos(@t+)Summary: If the body is subject to: A restoring force that is proportional to the displacement but opposite in sign( F = −kx ) ; or The acceleration is proportional to its displacement and of opposite sign( a x ) ; 2 = − or The motion equation is ; x = Acos(t +) k m x Fig.15 −1