An experimental engine oil has density 900 kg/m3, and its viscosity is being measured in a laboratory. A 1-mm-diameter steel ball bearing is released into a much larger, and transparent, tank of the oil (Figure 4.26). After the ball has fallen through the oil for a few seconds, it reaches terminal velocity. A technician records that the ball takes 9 seconds to pass marks on the container that are separated by 10 cm. Knowing that the density of steel is 7830 kg/m3, what is the oil's viscosity?