Abstract
This research focuses on fundamental and general studies of sound generation by rigid spheres or droplets falling vertically down to a water surface and by water flow in tubes. This first report aims to make clear phenomena and reasons of sound generation caused by a rigid nylon sphere, water droplet or droplets falling in series to a water surface. In case of a rigid sphere, it is shown that only the impulse sound consisting of one wave is generated for the wet sphere. But for the dry sphere about 30 ms after the impulse sound, sounds are generated by the cavity behind the cylinder caused by surface tension and the bubble. It is also shown that a droplet generates an impulse sound, but that when a following droplet impulses the water surface at the lowest instant of the indented part caused by the impulse of the preceding droplet, a bubble is formed in the water and generates sound.
