Not quite the Indian Rope Trick

A colleague of mine, Tom Mullin, showed that the predictions of the upside-down pendulum theorem really do work in practice, and that the critical frequency needed for the stability of the inverted state agrees well with that predicted by the theorem.



It is just possible, in fact, that some readers of this web page will have seen the inverted triple pendulum experiment, because we performed it on BBC TV's Tomorrow's World in October 1995.


At that time, our record was 3 pendulums on top of one another, each of length 19 cm, but Tom has subsequently managed it with 4 pendulums, just in time for us to demonstrate it in June 1997 at the Royal Society's public exhibition New Frontiers in Science.


Nature Vol 366, pp 215-216, 1993(with T. Mullin)

(See also Chapter 12 of From Calculus to Chaos or
radio interview with Thames Valley FM, 26 Feb 1998)






At the time, Tom Mullin and I conducted some rather more informal experiments with a length of net-curtain wire, which we reported briefly in New Scientist in 1998.
This work has recently been taken further in:

T Mullin, A R Champneys, B W Fraser, J Galan, and D Acheson
The 'Indian wire trick' via parametric excitation: a comparison between theory and experiment
Proc Roy Soc Lond A 459 (2003) 539-546.

and

J Galan, W B Fraser, D J Acheson and A R Champneys
The parametrically excited upside-down rod: an elastic jointed pendulum model
J Sound Vib 280 (2005) 359-377.


I have written some simulation software to accompany the second of these papers.



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