Enclosed electrostatic whirls

whirlThe classical electrostatic whirl is a rotor with points bent to one side mounted over a pin, so it can rotate easily. With the pin connected to a high-voltage power supply the rotor turns, in reaction to the ionic wind blowing from the points. The experiment typically requires quite high voltage (> 10 kV) and several µA of current. It is usually attributed to Mr. Hamilton, professor of Philosophy at the University of Dublin (Hamilton's "mill", or "fly"), from an article in the Philosophical Transactions by Benjamin Wilson relating the experiment in 1760 [1]. A friction electrostatic machine was used as power supply. It was known too [2][3][4] that if the whirl is enclosed by a glass box the rotation soon stops, and is restored if the glass is touched.

A curious variation of the electrostatic whirl can be obtained taking a square of aluminum foil or paper folded at the diagonals (a "chi spinner") and mounting it over a metal needle, so it is balanced and can move easily. The assembly shall allow the needle to be connected to a high-voltage supply and have space around for a glass pot covering the rotor, with the glass insulated (by plastic, that insulates better than glass) and not in contact with the ground or with the power supply. The glass must be dry and clean, presenting reasonably high insulation, but not too high. The DC power supply can be positive or negative, 5 to 10 kV. The required current is much smaller than with a classical whirl. The following properties can be observed:

 The reason of the rotation is probably the charge deposited inside the pot by the points of the terminal, repelling the points. Any small asymmetry starts a rotation, and as the glass is not a perfect insulator, the charge leaks away if the pot is not insulated, and the repulsion is continuous. The synchronization of two spinners is probably consequence of the rotating electric fields around the pots. The videos below show some of these experiments, and others:

The origin of the idea is this video.

[1] Benjamin Wilson, "Farther experiments in electricity," Philosophical Transactions of the Royal Society, Vol. 51, part II, 1761, pp. 896-906.
[2] Tiberius Cavallo, "A complete tratise of electricity," 4th ed. Vol. I, Dilly, London, 1795, p. 297.
[3] Augustin Privat-Deschanel, "Elementary treatise on natural philosophy," Blackie & Son, London, 1870, p. 579.
[4] Tomlinson, "Experiments on the electrical fly," Philosophical Magazine, Vol. 27, No. 181, pp. 202-218, March 1864.

Created: 6 February 2011
Developed and maintained by Antonio Carlos M. de Queiroz.

Return to Electrostatic Machines