At the end of the 1970 decade, computers to which we had an easy access were a few orders of magnitude slower then the PC on which I am preparing this page. Simulating many body systems on them was impossible. Attracted by the wonderful computer experiments made by Alder, Hoover at al. we did not like to quit. As a result of this frustrating situation an idea to create a mechanical, analog simulation of the hard-disk system was born. The simulator was created. It worked very well. The size of the system we could simulate was impressive - up to a few thousands disks.

What is needed to make the experiments:

1. a few thousands of steel balls - diameter around 3 mm,
2. a loudspeaker with a flat, stiff plate attached to its membrane,
3. an audio generator.
Design a flat boundary box whose shape and size can be varied and attach it to the plate.
Pour the balls into it.
Cover the box with a glass plate.
Put the box into vibration and observe their motion.

Using this experimental set-up we carried out a series of experiments. Their results are described in series of papers:

P. Pieranski, J. Malecki, W. Kuczynski and K. Wojciechowski,
A hard-disk system.  An experimental model.
Phil. Mag.,  37, 107 (1978).

P. Pieranski and J. L. Finney,
A hard-disk system.  Structures of a close packed thin layer.
Acta Cryst.,  A 35, 194 (1979).

P. Pieranski, J. Malecki and K. Wojciechowski,
A hard-disk system.  Solid-solid phase transition  in a thin layer.
Mol. Phys.,  40, 225 (1980).

K. W. Wojciechowski, P.  Pieranski, J. Malecki and P. Barnes,
A hard-disk system; An Ising-like behaviour in a thin layer.
Mol. Phys.,  42, 435 (1981).

K. W. Wojciechowski, P.  Pieranski and J. Malecki,
A hard disc system in a narrow box. .  I.  Thermodynamic properties.
J. Chem. Phys.,  76, 6170 (1982).

A. C. Branka,  P.  Pieranski and K. Wojciechowski,
Rotatory phase in a system of hard cyclic hexamers. An experimental modeling study.
J. Phys. Chem. Solids, 43, 817 (1982).

W. Wojciechowski, P.  Pieranski and J. Malecki,
A hard disc system in a narrow box. .  II.  An instability.
J. Phys.,  A 16, 2197 (1983).

P. Pieranski,
An experimental model of a classical many body system.
Am. J. Phys.,  53, 68 (1984).

Pieranski, K.Wojciechowski, A.Branka and M.Godlewska,
Metoda symulacji mechanicznej w badaniu klasycznych ukladów wielu cial,
Postepy Fizyki, 38, 757 (1988).

Other papers based partially on observations made in experiments with the mechanical simulator

B. Pansu, P. Pieranski and Pawel Pieranski,
Structures of thin layers of hard spheres.  High pressure limit.
J. Phys. (Paris), 45, 331 (1984).

A. Bonissent, P.  Pieranski and Pawel Pieranski,
Solid-solid phase transitions in a low dimensionality  system.
Phil. Mag.,  50, 57 (1984).

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