The apparatus has been designed to introduce students to the fundamental characteristics of the behaviour of the particle system, in particular the relationship between the drag coefficient of falling particles and Reynolds number. Particles covering a range of sizes and densities are supplied and the experiments are conducted by allowing single particles to fall through a number of different liquids contained in a vertical glass tube. The rate of fall of the particle is determined by timing their passage between two marks on the walls of the glass tubes. Observation of the particle movement is aided by the provision of a shielded fluorescent tube light mounted on the backboard. Particles can be removed from the bottom of the tubes without the necessity of draining the liquid. A valve system is provided at the bottom of each tube to allow the particles to be removed with the minimum loss of liquid.