Boyd F Edwards et al 2001 Eur. J. Phys. 22 113 doi:10.1088/0143-0807/22/2/302
Boyd F Edwards1, Joseph W Wilder2 and Earl E Scime1
Show affiliationsA standard undergraduate mechanics problem involves a raindrop which grows in size as it falls through a mist of suspended water droplets. Ignoring air drag, the asymptotic drop acceleration is g/7, independent of the mist density and the drop radius. Here we show that air drag overwhelms mist drag, producing drop accelerations of order 10-3g. Analytical solutions are facilitated by a new empirical form of the air drag coefficient C = 12R-1/2, which agrees with experimental data on liquid drops in the Reynolds-number range 10<R<1000 relevant to precipitating spherical drops. Solutions including air drag are within reach of students of intermediate mechanics and nonlinear dynamics.
92.60.Nv Cloud physics; stratus and cumulus clouds
92.60.Jq Water in the atmosphere (humidity, clouds, evaporation, precipitation)
Issue 2 (March 2001)
Received 28 October 2000
Boyd F Edwards et al 2001 Eur. J. Phys. 22 113
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