But Let me look at the interesting part of R A O of acceleration. Sometime you know, you want to find out acceleration here, you do not want to find out the motion, but acceleration, physically important because suppose there is a gun mound here, the load is going to be mass into acceleration. So, you are interested in acceleration. So, now, how do I found R A O for acceleration? My z, let say heave heave case, it was z A into how