Also known as the centrifugal force machine, it is a teaching aid used to show the effects of the centrifugal force that come into play when there is uniform circular motion.
It is composed of a rotating apparatus in which a sturdy, vertical, metal staff assembled on a wooden platform can be made to rotate, more or less rapidly, around its axis by means of a wheel or crank turned manually and a transmission mechanism with a belt and pulley or with pinion and gear wheels.
Different accessories can be attached to the drive shaft to perform several kinds of experiments.
In the exemplar presented here, the rotating mechanism is missing and only three accessories remain; they consist of a U-shaped brass frame (width 76.5 cm, height 13.5 cm). In one of the accessories the frame is closed at the top by an iron rod on which two ivory balls, one three centimetres in diameter and the other four centimetres in diameter, are free to slide.
With this accessory we can demonstrate the dependence of centrifugal force on the mass of the rotating body, on its distance from the rotation axis and on the speed of rotation.
In the other two accessories, which are used to demonstrate centrifugal force with liquids, the frame is not closed at the top but holds the recipients with the liquids in a suitable position.
One has at the centre a cylindrical recipient (height 11.5 cm, diameter 8 cm) which is filled with a liquid, which is usually coloured water, and which communicates, near the base, with the opening of two spherical bottles (diameter 10 cm) with a long, narrow neck (diameter 2 cm, length 22 cm), the bowls of which are held by two spherical brass caps attached to the vertical arms of the frame.
When the device is made to rotate, the liquid rises up to the bowls and then goes down when the rotation ceases.
The other frame has two glass tubes (length 38 cm, diameter 2 cm) containing water, closed at the base and sloping toward the centre, with one end attached to the centre of the frame and the other to the upper part of the vertical arms of the frame.
One of the two tubes contains a metal ball and the other a cork ball that floats on the water. When the device rotates, the metal ball rises to the top while the cork ball goes through the liquid down to the bottom. This difference in behaviour is due to the fact that with equal volume, metal has a mass greater than that of the liquid, while the opposite is true of cork.
Battelli - Cardani (1922), Vol. I, p. 149
Daguin (1878), T. I, p. 83
Privat Deschanel (1869), p. 65
Roiti (1887), T. I, p. 82