Post date: Apr 10, 2014 1:10:55 AM
A second order system can approximately behave like a first order system when it is over damped. In this case, the characteristic roots are real, and if the damping ratio is sufficiently large, one of the real roots will be much smaller than the other. The effect of the larger root on the response is negligible, and the second-order system approximately acts like a first order system.