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This 1 page Study Guide was uploaded by Usman Qureshi on Wednesday November 18, 2015. The Study Guide belongs to a course at a university taught by a professor in Fall. Since its upload, it has received 16 views.
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Date Created: 11/18/15
3 Last Lecture 3 Applications of Newton s Three Laws 3Today 3 Friction 3 Important Concepts 3 The magnitude of friction depends on the magnitude of the Normal force 3 The magnitude of friction depends on whether there is motion along the surface slipping or not slipping 3 The magnitude of friction has a maximum possible value 3 The coefficient of friction is often less when an object is slipping than when it is not slipping Important Reminders 3 Pset 3 due here tomorrow at 10am 3 If you want to discuss your exam or general class performance contact me or your recitation instructor during office hours or by appointment 3 Students are often hesitant to do this but it is strongly recommended Don t be intimidated we are here to help you and want you to succeed 3 No class next Monday or Tuesday 3 Next Mastering Physics due next Wednesday 3 Next Pset due next Friday Properties of Friction Magnitude 3Not slipping The magnitude of the friction force can only be calculated from Zizma However it has a maximum value of Ifl SLLSN 3Just about to slip f u N whereN is the Normal force and us is the coefficrent of static friction which is a constant that depends on the surfaces 3Slipping f u N where N is the Normal force and uk is the coefficrent of kinetic friction which is a constant that depends on the surfaces 3Note us zuk Properties of Friction Direction 3Always parallel to the surface 3lfthere is slipping friction acts in the direction opposite to the motion 3lfthere is not slipping friction acts in the direction needed to prevent motion 3 Note that it s not always immediately obvious what direction this is problems can get complicated Checklist for Friction Problems 3Slipping 3 Direction and magnitude of friction are unambiguous 3Just about to slip 3 Magnitude of friction is unambiguous 3 Not slipping 3 Magnitude of friction is totally unknown Use 2Fm 3 Just about to slip or not slipping 3 Direction of friction is opposite to direction it will slip 3 Find this direction by determining motion without friction 3Sometime obvious sometimes requires a calculation Summary 32Fm 2Fm 2Fm 3With friction pay close attention to whether there is slipping almost slipping or no slipping 3 The procedure to solve problems is very different in the three cases 3Think carefully about the direction of friction 3 Don t make the careless mistake of blindly substituting f 2 SN everywhere 3 Don t make the careless mistake of assuming you know the Normal force without checking other forces
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