The Viscosity and Particle Drag apparatus is a simplefalling-sphere viscometer. The self-standing unit holds two glass tubes filledwith the test fluids, for comparisons and to minismise draining and refillingof the fluids after experimentation. The back plate has a low-voltage backlightso students can easily see the test spheres through the fluid. Students fillthe two tubes with their chosen test fluid, then select a sphere of the correctdensity and size for the fluid. They drop the sphere into the test fluid at thetop of the glass tube. They then use a stopwatch (included) to measure the timetaken for the sphere to fall a set distance down the tube. When the test spherereaches the bottom of the tube, it enters a valve that the students turns,dropping the sphere into a collection vial for recovery. The valve systemminimises the fluid loss from the tube and helps when draining the tube afterthe tests are complete. Students may also make their own use shapes to test inthe unit. The shapes must fi t through the valve at the base (maximum 8 mm inany single dimension). Suitable test fluids include water, thin machine oil,castor oil and motor oil. The apparatus can be used with any fluid that can besafely handled and is chemically compatible with the wetted parts of theequipment - glass and PTFE.