| dc.description |
The author's vibrating plate method of forming powder ridges on a flat surface has now been used to study the phenomenon with graded powders of different densities and at different frequencies and intensities of vibration of the sound field. It is found that the distances between the ridges increase roughly as the square root of the particle diameters, a result which is in agreement with Bagnold's observations with powders under oscillating water, but needs still to be taken into account of in connection with Kundt powder ridges. `Granular' ridges, one particle wide, are nearer together than powder ridges, the spacings of which increase with the amount of powder which is present. Much larger intensities are required to move dense powders than light powders; the resulting spacings are, however, approximately the same. The variables which have most influence on the spacing are the diameters of the grains and the frequency of the vibration, not the intensity. These matters are discussed in relation to the phenomenon of `wavy' ridges. Experiments in which larger objects, as well as powders, are introduced into the field are also described. |
