Date: Tue, 22 Apr 2003 15:04:18 -0700

Author: Eric Ayars

Subject: Parametric oscillator: was exponential growth

Post:

>How about a parametric oscillator? For example, a pendulum whose length is
>varied by a small amount at twice the natural frequency of the pendulum.
>Starting from "zero" amplitude the oscillations build up in a dramatic way.

This is a new one for me: have any more details?
--

-----------------------------------------------------------------
Dr. Eric Ayars
Assistant Professor of Physics
Walla Walla College
ayars@mailaps.org
(509) 527-2476
http://homepages.wwc.edu/staff/ayarer
From rudd@sfu.ca Tue Apr 22 20:03:57 2003
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Date: Tue, 22 Apr 2003 17:05:49 -0800
Subject: Re: Parametric oscillator: was exponential growth
From: Jeff Rudd
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PIRA 3A95.60

see Flying Circus of Physics 2.58 and Maryland D3-12

We did this a long time ago, very crudely but it worked well. We hung a
string and bob from the shaft of a small synchronous motor, with the string
passing through a fixed washer just below the motor so that when the motor
was plugged in the bob moved vertically. The length of the pendulum was
adjusted so that the frequency of the motor was twice the frequency of the
pendulum. We used a motor that was handy, as I recall the length of the
pendulum was approx 80 cm. We plugged the motor in with the bob stationary.
The pendulum is self-exciting - any random motion of the bob is amplified.
The amplitude increases exponentially, our maximum was of the order of 90
degrees. The audience was impressed.

Jeff Rudd

> From: Eric Ayars
> Reply-To: tap-l@listproc.appstate.edu
> Date: Tue, 22 Apr 2003 15:04:18 -0700
> To: tap-l@listproc.appstate.edu
> Subject: Parametric oscillator: was exponential growth
>
>> How about a parametric oscillator? For example, a pendulum whose length is
>> varied by a small amount at twice the natural frequency of the pendulum.
>> Starting from "zero" amplitude the oscillations build up in a dramatic way.
>
> This is a new one for me: have any more details?
> --
>
> -----------------------------------------------------------------
> Dr. Eric Ayars
> Assistant Professor of Physics
> Walla Walla College
> ayars@mailaps.org
> (509) 527-2476
> http://homepages.wwc.edu/staff/ayarer
>
>
From cablem@wfu.edu Tue Apr 22 21:51:21 2003
Message-ID: <3EA5F29C.7020802@wfu.edu>
Date: Tue, 22 Apr 2003 21:55:40 -0400
From: Machele Cable
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To: tap-l@listproc.appstate.edu
Subject: Re: bumblebee
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Here's a list:
http://wings.avkids.com/Book/Animals/instructor/insects-02.html

Chele

Anthony Lapinski wrote:

>Anyone know the approximate frequency of a bumblebee (or other small
>flying creatures) flapping its wings? I'm trying to make up a
>beats/Doppler effect problem.
>
>
>
>
>

--
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Machele Cable Lab Manager Physics WFU
Phone: (336) 758-5532 Fax: (336) 758-6142
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There's a thin woman inside of me trying to get out,
but I can usually shut her up with some chocolate!


From britton@ncssm.edu Tue Apr 22 22:16:05 2003
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