There is something I do not understand from this quotation taken from an encyclopedia.quot;A device in which solid or liquid particles of different densities are separated by rotating them in a tube in a horizontal circleThe denser particles tend to move along the length of the tube to a greater radius of rotation, displacing the lighter particles to the other end.quot;The second sentence, describing the denser particles moving along the length of the tube to a greater radius of rotation, is a source of confusion to meWhen separating substances of different densities with a centrifuge, how are the substances layered after centrifugation? Are they stacked vertically, with the dense particles at the bottom and the least dense at the top? Or are they layered from the center? I have not seen a centrifuge in operation and so I have not seen for myself.
Assume you have a test tube, having a solution containing suspended particles of equal size and different densitiesFor example equal sized iron particles and aluminium particlesNow close the test tube with a cork.At this time, you will see the particles are mixed and are not separatedAssume that you have a small horizontal round table mounted on a motorWhen the motor rotates, the turn table will rotate about a vertical direction.The speed of rotation can be controlled by the speed of the motorTake the test tube and fix it firmly on the turn table.Now rotate the turn tableThis rotation causes a centrifugal force to develop and act on the particlesThis centrifugal force is proportional to the mass of the particles( mv^2/r where m is the of the particle, v linear velocity of the particle and r is the radius of the circular motion of the particle)Since the particles are of same size, it is proportional to the density of the particlesThe denser particles(iron) are subjected to a greater force and hence tends to move farther away from the centre of rotation, compared to the lighter particles ( copper)After certain time, all the iron particles collect at the bottom of the test tube while the lighter particles are collected just above the heavier particlesif you look from the turn table, heavier particles are collected farther away from the centreBut if you consider the test tube, they are collected at the bottom of the test tubeI hope now you can get a good idea of a basic centrifuge.
