Introduction

Abstract

The physical mechanism of the topic under investigation can be demonstrated by very simple experiments. Consider a transparent container (i.e., a beaker or a test tube) in the upright position, filled with water. A particle, small solid and “heavy” (i.e., its density is higher than that of the fluid in the container), is released from rest into the vessel. Under the action of gravity, buoyancy and viscosity (“drag”), the particle will quickly accelerate, then descend (“fall”) with a steady velocity and finally “settle” on the bottom of the container.