Lab Works or CBL and motion detector is great for this experiment or demo in
_Visualizing Chemistry_ ACS 1995, Different gases in a closed tube (one end).
The length of the tube changes. Simple math and the speed of sound in that
gas or for chemists - the molecular weight can be obtained with very good
results. Also a "Stanley Estimator" - real estate agents, capet installers use
them for room dimensions. Cheap at $35.
As we discovered several years ago, placing a piece of tissue over the
detector's receiver will absorb faint echos off of the sides of the tube. This
is also a great idea for all motion detector experiments as well.
The ChemBio workshops from Texas Instruments uses this as one of the projects
in the week long sessions
best jim and julie
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Packer Collegiate Institute
Brooklyn, NY USA