Vibration isolation

This demonstration compares forced vibrations of two glasses containing similar amount of water, one with and one without a plastic foam support, and shows the effect of base isolation.

Fig. 18-7: Altering structural frequency using base isolation

A medical shaker can be used as a shaking table to generate harmonic base movements in three perpendicular directions. A glass is fixed directly to a wooden board while a similar glass is glued to a layer of plastic foam which is mounted on the wooden board, as shown in Fig. 18-7.

Fill the two glasses with similar amount of water. When the shaker moves at a pre-set frequency, it can be seen that the water in the glass on the plastic foam moves less than that in the other glass. The difference is due to the effect of the plastic foam, which isolates the base motion and also produces a natural frequency of the glass-water-foam system which is lower than that of the glass-water system and is thus farther away from the vibration frequency.