Mechanical looseness shows up in the frequency domain as a large number of harmonics of running speed when lightly loaded. Typically ½ harmonics shows up, as 1½ X, 2½ X, etc. The harmonics show up because of clipping of the waveform when the loose parts hit against their limits of movement. The vibrating part is not allowed to swing to the full extreme of motion that it would like because it hits up against physical stops.
This experiment helps the student to understand the effect of looseness in rotating systems. Experiments can be done by virtually creating and removing mechanical looseness in a machinery. The vibration frequency and amplitudes can be compared to study the effect of looseness.