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On the groupings and general behaviour of solid particles under the influence of air vibrations in tubes

1931; Royal Society; Volume: 230; Issue: 681-693 Linguagem: Inglês

10.1098/rsta.1932.0012

2053-9258

E. N. da C. Andrade,

Experimental and Theoretical Physics Studies

In 1866 KUNDT showed, by a method described in every text-book of Sound, that if stationary waves are set up in the air in a long tube containing dust, then the wavelength is indicated by little collections of dust which form at the nodes. In addition to these dust heaps at the nodes there appear, when the air is thrown into strong vibration, a series of ridges or striations of dust, lying on the bottom of the tube at right angles to the axis. Photographs illustrating these ridges are appended to this paper, and will receive further reference at a later stage. The production of these striations (which were, of course, observed by all the earlier experimenters not while the air was in vibration, but after the vibration had ceased) was explained in 1891 by WALTER KOENIG, in a calculation of hydrodynamic forces, based on investigations of C. A. BJERKNES. KOENIG considered the case of two spheres in a vibrating fluid, and showed that if the line joining the centres of the spheres was parallel to the direction of vibration of the fluid there was repulsion between them, while if the line of centres was normal to the direction of vibration the spheres attracted one another. The force thus called into play varies inversely as the fourth power of the distance between the centres of the spheres, and directly as the square of the velocity of the fluid. It is assumed that the spheres do not share appreciably the periodic motion of the fluid—an assumption which is generally, but not always, reasonable for obstacles of the size and mass used, viz., particles of cork dust and the like.