Transient response with unit-step input Standard expression +250n立+o7y=ou(t) Roots are S1,2=±j0m c(t) y(t)=1-cos(@,t) 2 Free vibration Critically stable 5=0 Without damping零阻尼Transient response with unit-step input 2 2 2 () nn n   y y y ut        0 Without damping 零阻尼 Roots are n s 1,2   j  2 2 2 () () n n Ys Us s     y ( t ) 1 cos( t )   n Free vibration Critically stable Standard expression