Rolling friction. When an object rolls over a surface, the contact area of both the object and the surface can continuously deform and recover. Energy is lost in that continuous motion and thus the kinetic energy of the object gradually decreases. A rolling friction is said to act on the object. with a magnitude frgiven by fr = .UrFM whereby is the coefcient of rolling friction and FM is the magnitude ofthe normal force. In the gure below, a pool hall rolls rightward overthe felt of a pool table. The deformation ofthe ball is negligible but the deformation of the felt creates the rolling friction. The support forces along the contact area can then be represented by shifting the normal force PM rightward by distance h from being directly underthe center of mass. The torque due to that force about the centerof mass works against the rotation. The ball has mass m = 97.0 g and radius r = 26.2 mm. and the shift distance is h = 0.365 mm. [a] What is the magnitude ofthe torque due to the normal force? What is the change in energy due to the torque ifthe ball rolls through {bl one revolution and [c] distance L = 38.6 cm? (d) What is the value of ,ur? in 4H {a} Number 3.46e~4 Units me "' (b1 Number H 2.172 Units [c] Number n 5097 Units {d} Number a 0.1389 Units lll