SOLUTION A turntable is set rotating at a constant frequency of 45 rpm (revolutions per minute). A nickel is placed on the turntable near the axis of rotation at a distance r from that axis. The nickel is observed to rotate around in a circle of radius r with a frequency of 45 rpm. The nickel is pushed slightly away from the axis of rotation, thereby increasing the value of r. This is repeated until r is so large that the nickel just slides right off of the turntable. The largest value of r such that the nickel remains in circular motion on the turntable without slipping of is found to be rmax = 7.8 cm. From these data, determine the coefficient of friction between the nickel and the turntable.