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Physics of Maximum Amplitude versus Driving Frequency Question made in EJS post and replies

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Physics of Maximum Amplitude versus Driving Frequency Question
lookang Avatar
lookang
222 Posts

Physics of Maximum Amplitude versus Driving Frequency Question referring an original model found in EJS examples found in.....\source\users\davidson\wochristian\osc\SHOResonance.xml

Dear Prof Wolfgang,

i am puzzled as to the correct ODE equation for the driving force's acceleration component.

is it

+A*Math.cos(omegaD*t)/m 

or

+A*Math.sin(omegaD*t)/m .

 

the resultant plots for +A*Math.cos(omegaD*t)/m starts at Amplitude =1 which is what i believe is correct but it does not have the maximum curve characteristics (see picture) 

 

for case 2: the resultant plots for +A*Math.sin(omegaD*t)/m starts at Amplitude =0 which is what i believe NOT correct but it has the maximum curve characteristics (see picture).

 

Any advise how i can model the driving force such that

1) start at Amplitude= 1 (usually we teach with a non-zero value in our lecture notes)

2) has the desired maximum curve characteristics which exists in our teaching materials (usually we do teach this feature).

 read more:

http://weelookang.blogspot.sg/2014/03/ejs-resonance-frequency-vs-amplitude.html

 

model DL here

https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejs_model_SHOResonancewee.jar

 

source is also attached for consideration into the OSP collection please

 

thanks!

Post edited March 19, 2014 at 11:04 PM EST.

Attached File: ejs_src_SHOResonancewee.zip


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Replies to Physics of Maximum Amplitude versus Driving Frequency Question

Re: Physics of Maximum Amplitude versus Driving Frequency Question -
Wolfgang
146 Posts

Both sine and cosine forms for the driving force should give the correct result.  The problems seems to be that that model does not measuring the maximum amplitude directly.  Using the energy to estimate the maximum amplitude is incorrect when the damping is large.



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