The exam boards for A-level physics require or suggest a number of practical activities that will allow you to satisfy the Common Practical Assessment Criteria (CPACs). Among other requirements, you are expected to be able to make accurate observations relevant to the experiment, to obtain accurate, precise and sufficient data, and record these methodically using correct units and conventions, and to use ICT with appropriate software to process data. Measuring the time taken for a ball-bearing to fall a given distance, as well as finding the density of the liquid and the diameter and density of the ball-bearings, gives practice in making careful measurements. Using the calculated values of terminal velocity and density and the measured radius to determine the dynamic viscosity of the liquid gives practice with ICT and analysis skills.
Dynamic viscosity, η,is the measure of how resistant a fluid is to deformation at a given rate. It can be thought of as a measure of how ‘thick’ or ‘sticky’ a fluid is. The SI unit of dynamic viscosity is the newton-second per square metre (Nsm –2), or the equivalent unit, pascal-second (Pa s — see Crossword notes, pp. 30–33).
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