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From the basic definition of velocity, an estimate settling velocity of the particles can be expressed as a function of displacement (z) divided by time (t): (EQUATION: Vs=z/t)
(1.1)
In the case of this experiment, z will be the maximum distance between the bottom of the ball valve and the measurement volume of the turbidimeter: 16 cm. With the two settling times already chosen as 5 and 20 minutes, estimate settling velocities of 0.533 mm/s and 0.133 mm/s were calculated.
Settling velocity can also expressed in terms of gravity (g), particle diameter (D), particle density (ρbead in this case), water density (ρH2O), and the kinematic viscosity of water (ν):
(1.2)***EQUATION
The density of the beads given when purchased was 1.05 g/cm3 and the water density and kinematic viscosity are already known to be 1000 kg/m3 and 1.004e-6 m2/s. Relating equation 1.1 and 1.2, the diameters of the two beads were found to be about 140.159 μm and 70.014μm.
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