Chapter 10321P10.87Rolling is instantaneous rotation about the contact point P. Theweight and normal force produce no torque about this point.Now F1produces a clockwise torque about Pand makes thespool roll forward.Counterclockwise torques result from F3and F4, making thespool roll to the left.The force F2produces zero torque about point Pand doesnot cause the spool to roll. If F2were strong enough, it wouldcause the spool to slide to the right, but not roll.F1F2F3F4θcPFIG. P10.87P10.88The force applied at the critical angle exerts zero torque aboutthe spool’s contact point with the ground and so will not makethe spool roll.
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