*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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