Observing the effect of damping in free vibrations

This set of models demonstrates the effect of damping provided by oil in free vibration, which can be observed by eyes.

         
(a)                                                               (b)
Fig. 17-2: Effect of the damping provided by oil.

Take a steel ruler and form a cantilever as shown in Fig. 15-9a. Give the tip of the ruler an initial displacement and release it. The steel ruler will perform many cycles of oscillation before it becomes stationary indicating that the damping ratio associated with steel alone is low.

Fig. 17-2a shows two identical steel strips acting as cantilevers. The only difference between the two cantilevers is that connected to the free end of the cantilever on the left is a vertical metal bar which in turn is attached to a disk immersed in oil. Fig. 17-2b shows the disk by lifting up the free end of the strip. Thus the effect of the oil and the device can be examined.

Press the free ends of the two cantilevers down by the same amount and then release them suddenly. It will be observed that the cantilever on the left only vibrates for a small number of cycles before stopping while the cantilever on the right oscillates through many cycles demonstrating the effect of viscous damping provided by the oil.