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 Author Topic: Oscillations Damped and forced oscillations by Wee Loo Kang  (Read 22805 times) 0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).
Fu-Kwun Hwang
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 « Embed this message on: July 26, 2007, 11:35:20 pm »

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Objective
9745 H2 PHYSICS (2008) 8. Oscillations Damped and forced oscillations: resonance (k) describe graphically how the amplitude of a forced oscillation changes with frequency near to the natural frequency of the system, and understand qualitatively the factors which determine the frequency response and sharpness of the resonance.

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Resonance
For a forced oscillation, when the driving frequency is equal to the natural frequency of the oscillating system, maximum energy is transferred from the periodic force (driver) to the oscillating system which will vibrate with maximum amplitude. This phenomenon is called resonance.

Frequency Response Graph (under different degrees of damping)
The Effect of Damping on Forced Oscillations
When damping is present, it reduces the amplitude (y-axis) of the forced oscillation for all driver frequencies (x-axis) and it causes the maximum amplitude to be reached when the driving frequency is a little less than the natural frequency.
This reduction in amplitude is more significant at the resonance frequency and frequencies close to it, so that we say damping reduces the sharpness of resonance -- that is, the oscillating system responses little (small change in the amplitude) over a wide range of frequencies.

This Interactive Resource was designed by: Wee Loo Kang

Using Easy Java Simulation by : Francisco Esquembre

Thanks to Fu-Kwun Hwang & Francisco Esquembre for their expert advise in (EJS):
Using Forum on EJS:http://www.phy.ntnu.edu.tw/ntnujava/index.php

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lookang
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 « Embed this message Reply #1 on: July 26, 2007, 11:52:53 pm » posted from:Singapore,,Singapore

i had this situation too when i publish html

Prof. Hwang, can resize the applet to maybe smaller? the plot buttton is hidden ?

width="750" height="550"

to fit into firefox browser. Thanks
 « Last Edit: July 27, 2007, 12:13:50 am by lookang » Logged
Fu-Kwun Hwang
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 « Embed this message Reply #2 on: July 27, 2007, 08:27:46 am »

I have to modify the source to change the view to make it really work.
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lookang
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 « Embed this message Reply #3 on: July 27, 2007, 09:10:07 am » posted from:Singapore,,Singapore

b = 0 frequency response
no damping
 « Last Edit: July 27, 2007, 09:40:49 am by lookang » Logged
lookang
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 « Embed this message Reply #4 on: July 27, 2007, 09:23:34 am » posted from:Singapore,,Singapore

b = 0.1
moderate damping

maybe (0.2, 0.4~) is an anonymous data !!?

redo to verify it yourself and replot
 « Last Edit: July 27, 2007, 09:48:41 am by lookang » Logged
lookang
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 « Embed this message Reply #5 on: July 27, 2007, 09:33:29 am » posted from:Singapore,,Singapore

b=0.05
light damping
 « Last Edit: July 27, 2007, 09:41:13 am by lookang » Logged
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 « Embed this message Reply #6 on: July 27, 2007, 09:39:48 am » posted from:Singapore,,Singapore

b=0.5
heavy damping
note that the scale for the y axis is different

combine the graph into a common scale with get something like

the time to do these activities may be very long, some may argue no efficient for learning purpose.

I would argue for a compromise, let students engage in some activity (length of doing depends on foundation of learners) and move on to synthesis of the BIG picture
 « Last Edit: July 27, 2007, 09:46:49 am by lookang » Logged
lookang
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 « Embed this message Reply #7 on: July 27, 2007, 09:54:35 am » posted from:Singapore,,Singapore

my source

Prof.Hwang, the copy on the forum seems to be NOT plotting the frequency response.

Is my version more suitable where the applet is used as a cognitive tool for users to "conclude patterns"
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The most important medicine is tender love and care. ..."Mother Teresa(1910-1997, Roman Catholic Missionary, 1979 Nobel Peace Prize)"