Sedimentation is the separation of solid particles from fluids under the gravitational force. When a solid particle moves in a fluid. Then a number of forces are acting on it:
The gravitational force, acting downward.
The buoyant force, acting upward.
The drag force, acting upward. When a particle fall in a fluid under constant force, e.g. force of gravity, then particle accelerates for some time, but when the accelerating force equals the retarding force (Buoyant force and Drag force) then the resultant force acting on the particle will be zero, and particle quickly reaches velocity, which is the attainable under the circumstances and which is called the terminal velocity.
Free settling is that in which the motion of one particle is unaffected by the motion of the other particle while in case of hindered settling many particles are present so there is mutual interference in the motion of the particles and the velocity of motion or rate of settling is reduced.
The present set-up with 5 Nos. of Borosilicate Glass Graduated Cylinders is designed to study the zone settling depending upon the concentration and characteristics of the particles. These cylinders can be easily removed for cleaning. Rate of change in height of the various liquids/solids interfaces with respect to time can be measured with the help of stop watch.