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Re: [Phys-l] mechanical (Applies to all, I presume.) on reflection question.



Brian!

My memory returned. I opened my image sequence in QT-7 pro and saved it as a .mov w/one FPS. It's in Someone_is_ wrong:


http://www.cleyet.org/Someone_is_Wrong/Shive%20machine%20(al%20fresco)/

Now one may step frames, and see that the end is quasi-free. This is occupying so much time, I must pull down from the top shelf in the garage my Shive machines! I also now remember w/it is a alligator clip soldered to a rod with a weighted base in addition to a motor driven crank.

Your clips work well. (They are similar to the one I posted to PTSOS.)


"Gummi bears, and other gummi candy, stick to teeth and may cause tooth decay.[12] However, gummi bears containing the cavity-fighting additive xylitol (wood sugar) are now being tested.[13]" Includes etymology:

http://en.wikipedia.org/wiki/Gummi_bear

The prob. w/the cheap (as in shoddy) al fresco machine is it's low Q. The pulse spreads (reminds me of QM animations.) and I suspect there's dispersion. For not too much added expense I recommend steel tape. C & H surplus sold feeler gauge tape in rolls. Steel strapping tape may have too much shear modulus w/o a large rod moment of inertia. Perhaps packaging tape would work better than masking tape and still has
the advantage of a sticky side.


Inverted vs. phase reversed: Would Pi change of phase be OK?

Yes a Z match would have no reflection like a term. resistor on a strip line, co-ax, etc. So It's impossible to terminate a line for no reflection w/o complete absorption. There must be a proof here.

bc


On 2011, Jan 30, , at 16:07, brian whatcott wrote:

BC, you show a movie of an 'al fresco' version of the Shive machine,
which was designed to provide a visual illustration of slow transverse
wave propagation and reflections. I am afraid your note does not specify
if the movie shows the effect of a fixed, or of a free end. The
illustration I provide (below) has three still pictures showing the
effect of a fixed or a free end. [If your browser does not depict these
three still pictures across the width of your display, you may find the
description confusing.]

The fixed end reflects an inverted pulse (not 'phase-reversed' as
described) whereas the free end reflects an isopolar pulse.
An end provided with the same acoustic impedance as the loaded
transmission rod would be expected to minimize reflections of either type.

<http://www.physics.umd.edu/lecdem/services/demos/demosg3/g3-03.htm>


Brian W