The study of free rise of buoyant spheres in gas reveals the universal behaviour of free rising rigid spheres in fluid in general

摘要

Since ancient times people have been trying to understand the nature of the forces governing the free fall of different objects in gas or liquid. Closely related to it is another type of free motion of bodies in a fluid, usually liquid: the free rise of buoyant fluid or rigid particles such as gas bubbles, ice crystals, wood particles, cork, etc. Galileo Galilei was the first who identified the driving force (the particle-fluid density difference) of both free fall and free rise (Galilei, 1590), as well as the force acting against it (i.e., friction) (Galiiei, 1638). On the basis of the balance of these forces, Galileo was the first researcher who assumed that a free rising buoyant sphere (for example, inflated bladder rising in water) would move exactly the same way as a free falling heavy sphere (stone in water). Since the publication of Galileo's works, it has been universally assumed, explicitly or not, that free fall and free rise of rigid particles should have similar motion properties (Newton, 1760; Knudsen and Katz, 1958; Munson et al., 1990; White, 1999).