From Newsgroup: sci.physics

Hi, I am playing around with model spring-mass-damper systems on my
analog computer. I was wanting, for comparison purposes, to make an
actual system with a spring and a mass. But I am a little confused how I
would know what the damping coefficient and spring coefficient is for
any given spring, as that doesn't seem to be listed for any springs I
can purchase on the Internet. Is there some catalog of springs out there
that lists those coefficients, or a way to calculate them from some
other listed parameter, or a practical way to measure them?
--
Christopher Howard
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From Newsgroup: sci.physics

Spring catalogs will list nominal spring constants but there's lots of variation. Better to measure your particular spring. As far as I know
nobody publishes damping coefficients. You could compute them from the
spring dimensions and the material properties but I don't think that
would be very accurate.

You can measure the spring constant by measuring the spring, applying a
known force, and measuring again. The spring constant is the force
divided by the change in length.

Knowing the spring constant you can then hang a mass from it, start it oscillating, measure the period and decay time constant, and calculate
the damping coefficient. That way you would be including the effects of
the air. Hang it from something rigid and massive, of course.
--
John Hasler
john@sugarbit.com
Dancing Horse Hill
Elmwood, WI USA
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From Newsgroup: sci.physics

John Hasler <john@sugarbit.com> wrote or quoted:

You can measure the spring constant by measuring the spring, applying a
known force, and measuring again. The spring constant is the force
divided by the change in length.

Knowing the spring constant you can then hang a mass from it, start it >oscillating, measure the period and decay time constant, and calculate
the damping coefficient. That way you would be including the effects of
the air. Hang it from something rigid and massive, of course.

Yeah, that makes sense.

I'm probably overthinking this kind of stuff. My first idea was to
record the curve and fit it to figure out those parameters.

But how would you even record a curve? You could film the
oscillation with a smartphone on a tripod. After that, you can
grab the individual frames using ffmpeg. The data's pretty easy to
analyze automatically if you highlight the moving part of the spring
- like by sticking a small light on it and filming in the dark.

Possible expression for fitting: a exp( -bt )cos( ct + d )+ e.

Possible software for fitting: Python (SciPy + NumPy + Matplotlib),
MATLAB, LabVIEW, or GraphPad Prism.


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From Newsgroup: sci.physics

https://en.wikipedia.org/wiki/Harmonic_oscillator#Damped_harmonic_oscillator

https://en.wikipedia.org/wiki/Mass-spring-damper_model
--
John Hasler
john@sugarbit.com
Dancing Horse Hill
Elmwood, WI USA
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