Question

What are damped vibrations ? How do they differ from free vibrations ? Give one example of each.

Answer 1

Harmonic oscillations tend to die away as time goes on. This behavior, called damping of the oscillations, is produced by forces such as friction and viscosity. These forces are known collectively as dissipative forces because they tend to dissipate the potential and kinetic energies of macroscopic bodies into the energy of the chaotic motion of atoms and molecules known as heat.
Difference between Forced vibration and Damped vibration
Forced vibration:
If a system is subjected to an external force, the resulting vibration is known as forced vibration if the frequency of the external force coincides with one of the natural frequencies of the system, a conditions known as resonance occurs (large oscillation). Failures of such structures as building, bridges, turbines and airplane wings have been associated with the occurrence of resonance.
Example - Musical instruments, Reed instruments and loudspeakers are good examples of forced vibrations.
Damped vibration:
If any energy is lost or dissipated in friction or other resistance during oscillation, the vibration is damped vibration.
Example - Vibration damping is used in industrial, electronic and ergonomic applications when there is a need to reduce the amount of energy that is produced by the system. Normally engineers try to address and reduce this energy at its source so the disturbing force is not at or near a natural frequency. This will ensure that resonance does not occur. Sometimes this is not possible for many reasons so problems will usually be controlled with a vibration damper. Usually when a good vibration damper is added, the energy that is left over is removed and converted to a small amount of heat which is referred to as the swallowed energy.