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http://microgroupstore.com/hypodermic-tubing.html
David Morin has hanging and falling chain problems in his text, see page 170. Also worked examples at the end of that chapter
If Biggins is correct, then there should be a measurable variation in the normal force at the bead launch rate, and (easier I suspect) the time integral of the normal force (steady state) should have an additional term of alpha*m*v where m is mass transferred in that interval. In other words there is an additional impulse of alpha*(mv). We should look for this as well as the ac component, which we can average using period folding once rate is known. We can get bead rate from video motion capture or acoustic pickup, see below.
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Feb 23 2014
extension ideas:
funnel at top to establish launch boundary conditions
acoustic pickup at bottom to get rate
electrical contact through chain to establish time of first contact at bottom
piezo trigger at bottom to get time of first contact