Immagini

DESCRIPTION

Exhibit 756 is an apparatus for demonstrating the nature of elastic collisions in which both energy and momentum must be conserved. It is composed of a rectangular wood base on which is mounted a wood column that sustains a rectangular frame. Seven ivory spheres are suspended from this frame each with two strings whose lengths are adjustable until all the spheres are in line and at the same height and touch each other at rest.

If one raises and lets fall one of spheres in the end positions, one notes that only the sphere on the opposite end seems to have received the energy and momentum of the falling sphere. If one raises and lets fall together two spheres on one end, one notes that only two spheres on the opposite end react, and so on. The case of one sphere before and after the collision is illustrated in design-1.

In practice the collisions are not perfectly elastic: the friction between the spheres is not zero and often the spheres assume some rotational movement, especially if the two strings support the spheres in a single point as evident in the photos. In practice after some collisions, the total energy is dispersed among the spheres which eventually come to rest.

BIBLIOGRAPHY

• [1] J.D. Gavenda and J.R. Edgington, "Newton's Cradle and Scientific Explanation", The Physics Teacher, Vol.35, Oct.1997.page 411.
• [2] Oreste Murani,"Trattato Elementare di Fisica", Volume primo, Ulrico Hoepli, Milano, 1922. Pagg. 232-233

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