Apparatus to illustrate the composition of movements

126.7 x 85.4 x 36
Carved and inlaid wood, brass, steel and lead

CAT. 1824 : F.IV.49

Um apparelho que serve para mostrar, que um corpo actuado por duas forças, que formem um angulo, descreve a diagonal d'um parallelogrammo formado sobre as direcçoens das duas forças. Tem tres espheras, duas de chumbo e uma de madeira, de cada uma das ques se pode usar como quizer.

An apparatus that serves to show that a body activated by two forces, which form an angle, describes the diagonal of a parallelogram formed under the direction of the two forces. It has three spheres, two of lead and one of wood, each one of which can be used as one wishes.

This machine comprises a vertical square of wood, in which one of the diagonals is inlaid in a light coloured wood, contrasting with the dark tone of the apparatus. The square is mounted on a beautifully worked wooden stand. This set of apparatus includes three spheres, two of lead and one of wood.

Over the upper side of the square there are two quadrangular iron bars parallel to each other. An iron cylinder, whose axis is horizontal and perpendicular to the bars, can move along them. In the upper right corner of the square there is a metallic piece where a cord is bound that passes through a groove in the lateral surface of the cylinder. From the other end of this cord, one of the spheres from the set is suspended. The cylinder has a small ring where a second cord is fixed, which passes through a pulley in the upper left corner of the square and which has a weight suspended from it.

Instruments of this type were currently used in physics laboratories of the 18th century and were intended to illustrate, by means of simple considerations of geometry, the composition of velocities in the case of uniform movement.

The apparatus illustrates what happens in a situation of equilibrium, that is, when equal weights are suspended from the two cords. Because of the restriction imposed by the length of the cord, the sphere will always be on the diagonal of the square, whatever the position of the cylinder. If the cylinder is given uniform movement, the following is observed: when the cylinder is moved to the left or to the right, the weight suspended from the cord that passes through the pulley falls or rises accordingly. Simultaneously, the sphere rises or falls. Since the sphere always moves along the diagonal of the square, it is possible to illustrate the composition of its movement, based on the vertical and horizontal projections of velocity.

The purpose of the apparatus, according to the 1824 catalogue, was to illustrate the rule of the parallelogram of forces; however, the apparatus does not allow this objective to be achieved. It is possible that the term "force" is used inadequately.

Nollet, Jean-Antoine, Leçons de Physique Expérimentale, Paris, 1764, Tomo II, Leçon V, P1. 2, Fig. 8.

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