Somehow I have become confused about the different parameters of a damped mass-spring system that follows: my'' + cy' + ky = 0 When the mass-spring system is oscillating, but passing through its equilibrium position (y=0), the third term will be zero. And from the best I can rationalize, the acceleration is also zero at this point and the velocity is maximal. Thus the first term is zero and the second non-zero. So I am left with one non-zero term equal to zero. Where is the flaw in my reasoning? Thanks.