The drag on a sphere moving in a fluid is known to be a function of the sphere diameter, the velocity, and the fluid viscosity and density. Laboratory tests on a 4-in.-diameter sphere were performed in a water tunnel and some model data are plotted in Fig. For these tests the viscosity of the water was 2.3x10-5 lbf s/ft2 and the water density was 1.94 slug/ft3. Estimate the drag on an 8-ft-diameter balloon moving in air at a velocity of 3 ft/s. Assume the air to have a viscosity of 3.7x10-7 lbf s/ft2 and a density of 2.38x10-3 slug/ft3. Assume Reynolds number similarity.
