Question about units for angular velocity, time constant

AI Thread Summary
The discussion centers on the relationship between angular velocity, time constants, and their units. It highlights that while a radian is dimensionless, converting natural frequency from rad/sec to cycles/sec yields different results when inverted to find time constants. The ambiguity arises in choosing between sec/cycle and sec/rad, as both can lead to valid but differing outcomes. The distinction between time constants, which indicate system response, and periods, which represent the duration of one cycle, is emphasized. Clarification on when to use each unit is sought, indicating a potential misunderstanding of these concepts.
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Here is a link to page in a book which contains an example problem:

http://imgur.com/OPrlw.jpg"

In the book, they work out the natural frequency of a hydraulic cylinder and come out with an answer in rad/sec. This number is then inverted to get a time constant, and the resultant unit is seconds.

I understand that a radian is dimensionless, and 1 rad/sec really equals 1/sec. So, it makes sense that you invert it and get seconds. However, you would also get seconds if you first convert the frequency from rad/sec to cycle/sec, and then invert.

My question is: how do you know which to use? When do you want to use sec/cycle, vs. sec/rad? It seems ambiguous, and the numbers would come out very differently.

I know the result of this equation is in radians. What if you experimentally measured the natural frequency in cycles/sec, and then inverted to get the time constant in seconds? You would get a different answer, but I don't think anything was done wrong.

Can anyone shed some light on this? I think I am missing something.
 
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I think you may be confusing a "time constant" vs. a "period." One is a parameter which is indicitive of a system's response, the other is the length of time for one cycle.

http://en.wikipedia.org/wiki/Time_constant

http://en.wikipedia.org/wiki/Period_(physics )
 
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