ABSTRACT
Figure 2-5 also shows that the phase angle of a real spring is not zero for all frequencies, but rather "jumps" between zero and pi radians. This was also confirmed in the measurements. To compare the pure/ideal and real behavior more closely we show a "zoomed" version of the amplitude ratio in Fig. 2-6. We see that the pure/ideal model is reasonably accurate up to about 150 rad/sec (24Hz). Note also that at about 830 radjsec the amplitude ratio drops theoretically to zero (again this is caused by the tangent function's behavior). This is called an antiresonance and physically means that at this frequency it takes a huge force to cause even a small motion. Again the measurements show that we don't get a "perfect zero" here; however, the amplitude ratio does drop to a value several hundred times smaller than Cs.
