# Question on Dynamics

1. May 19, 2006

### jrm2002

Question on Dynamics

I have been reading Structural Dynamics by Anil K. Chopra and am currently on the topic “Response of a Single Degree of Freedom System to Harmonic Excitation.

Can anyone help me with following clarifications??

1. Consider the Displacement Response Factor:
It is the ratio of dynamic deformation amplitude to static deformation amplitude. Now, when the ratio of the forcing frequency to the natural frequency of the system (Single Degree of Freedom System) is less than one (indicating a gradually varying force) then this displacement response factor is only slightly greater than one indicating that the contribution due to dynamic effects is negligible. Right?

Then when the ratio of the forcing frequency to the natural frequency of the system (Single Degree of Freedom System) is very much greater than one (indicating a rapidly varying force) then this displacement response factor approaches zero. Again there is no contribution due to dynamic effect.

Only when the ratio of the forcing frequency to the natural frequency of the system (Single Degree of Freedom System) approaches one (approaching resonance) the dynamic effect becomes dominant and damping plays a significant role? Right?

Does this mean one should worry about the dynamic response (as far as dynamic deformation is concerned) only in case of resonance (considering harmonic excitation)??