FIGURE 6.18 The operation of a centrifuge. The high centripetal acceleration requires a large normal force, which leads to a large apparent weight.
The ultracentrifuge is an important tool for separating and analyzing proteins in biological research. Because of the enor mous centripetal accelerations that can be achieved, the apparatus (see image) must be carefully balanced so that each sample is matched by another on the opposite side of the rotor shaft. Any difference in mass of the opposing samples will cause a net force in the horizontal plane on the shaft of the rotor; this force can actually be large enough to destroy the centrifuge. Suppose that a scientist makes a slight error in sample preparation, and one sample has a mass 10 mg greater than the opposing sample. If the samples are 10 cm from the axis of the rotor and the ultracentrifuge spins at 70,000 rpm, what is the magnitude of the net force on the rotor due to the unbalanced samples?
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