The main objective of this project is to demonstrate the effect coupling has on the natural frequencies and critical speeds of a disk-shaft system. To do this, our team experimentally, analytically, and numerically found the natural frequencies (or modes) of the rig with minimal percent errors. This must be done in a static and rotational reference frame in order to determine the critical speeds of the rotating disk-shaft system (the rotational velocity of a system when it rotates at a frequency exciting one of its natural frequencies). Our team analyzed the effects that varying disk geometries (diameter and thickness) have on the mode shapes and corresponding natural frequencies of the rig while maintaining a constant disk mass of 1.12 kg. From this information we drew comparisons between experimental and analytical results. We then made an assessment as to whether existing approaches to characterizing the dynamic response are always adequate or if there are specific regimes in which the model breaks down.