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-   -   [Help] Physical Explanations On Resonance Needed ? (http://www.molecularstation.com/forum/physics-forum/38296-%5Bhelp%5D-physical-explanations-resonance-needed.html)

 CSL 05-19-2006 04:09 AM

[Help] Physical Explanations On Resonance Needed ?

Hello, I want to ask a question about natural frequency of a simple,
undamped spring-mass system under forced vibration.

As textbooks tell us, when the forcing frequency is matched with the natural
frquency of the system, vibration resonance is achieved and as a result the
vibration amplitude is amplified to an infinitively large value.

My questions are:

1. In resonance cases, where does the large vibrating energy come from ?

2. In non-resonance cases, the vibration amplitudes are relatively smaller.
Where does the vibration energy go?

Textbooks illustrate these phenomena quite clearly through equations. But I
want to know more on the physical side. Does anyone here give physical
explanations?

Thanks.

CSL

 N:dlzc D:aol T:com \(dlzc\) 05-19-2006 04:31 AM

[Help] Physical Explanations On Resonance Needed ?

Dear CSL:

news:446d44ea\$1@127.0.0.1...

From the "forcing" source. The mass is simply a "piggy bank" for
kinetic then potential then kinetic... energy.

You find that not as much energy is put into the system since,
off resonance, the force and the motion are out of phase (or not
as much in phase). So with the mass moving counter to the
driving force (part of the time), energy is *taken out* of the
mass.

I hope that helps.

David A. Smith

 CSL 05-19-2006 10:06 AM

[Help] Physical Explanations On Resonance Needed ?

Thanks a lot. So, I can assume the infinitively large vibration amplitude
at reasonance is a result of vibration after many many many cycles. Right ?

 N:dlzc D:aol T:com \(dlzc\) 05-19-2006 01:09 PM

[Help] Physical Explanations On Resonance Needed ?

Dear CSL:

news:446d98a8\$1@127.0.0.1...
....

"infinitely"... an infinitive is something else.

Infinitely many cycles, right. And real physical systems break
long before... sometimes after just a few cycles. In fact, real
physical systems have non-linear springs, always have non-linear
damping, and masses that are distributed rather than point.

David A. Smith

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