福4.1Sliding FrictionCharacteristics ofstatic slidingfriction:1.Along the common tangent of the contact, reverse to the relative slidingtrend2.Magnified:0≤F≤Fm3.Fm=fF（Coulomb'slaw offriction）1Characteristics of dynamic sliding friction:1.Along the commontangent at the contact, opposite to the relativemovementdirection;2.Magnified: Fa = f'F f'< f
Characteristics of static sliding friction: 2 .Magnified： 3. （Coulomb's law of friction） 2 .Magnified： Characteristics of dynamic sliding friction: 1.Along the common tangent at the contact, opposite to the relative movement direction; 4.1 Sliding Friction 1. Along the common tangent of the contact, reverse to the relative sliding trend;
4.21Friction angle and self-locking phenomenon一、Friction angleFZWhen there is friction, the reaction force of thebearing against the balanced object includes normalRreaction/force N and tangential friction force F.TheCNresultant force of these two forces is called the fullconstraint reaction force of the bearing surface, i.e.R- N+Fand the angle @e bearing surface willchange with the &kFforce.Whentheobjectis in critiefinequilimreaches a maximumPNhen Omis called thevaluem,as showRPfriction angle.mNR
FR FN Fs T When there is friction, the reaction force of the bearing against the balanced object includes normal reaction force and tangential friction force . The resultant force of these two forces is called the full constraint reaction force of the bearing surface, i.e. , and the angle between it and the bearing surface will change with the change of the main force. When the object is in critical equilibrium, the angle reaches a maximum value , as shown in the figure, then is called the friction angle. N F R N F = + m N m Fm R m 4.2 Friction angle and self-locking phenomenon 一、Friction angle m Fm N R F N R