Dynamics: Free Vibration

Mode shapes of a continuous model

This demonstration shows the shapes of the first two modes of vibration of a continuous beam.

a) The first mode of vibration                      b) The second mode of vibration
Fig. 15-12: Mode shapes of a cantilever

Take a long plastic strip and hold one end of the strip as shown in Fig. 15-12. Then move the hand forward and backward slowly, it generates the first mode of vibration as shown in Fig. 15-12a. Do the same but increase the speed of the movement, it excites the second mode of vibration as given in Fig. 15-12b. The two mode shapes of the strip are similar to those shown in Fig. 15-7.