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This 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 17 views.
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Date Created: 11/18/15
3 Last Lecture 3Newton s Three Laws 3 Today 3More discussion 3Lots of examples 3 Important Concepts 3Think carefully about what object each force acts on 3Think carefully about which forces have well defined values and which one you need to calculate from Fma 3Think carefully about the acceleration Important Reminders 3 Pset 3 due Friday at 10am 3 Exam 1 average 64 3 Final class grade will be on a curve 3We don t give letter grade equivalents on individual exams General guidance is gtgt80 is good lt60 is not good lt45 is poor 3 If you want to discuss your exam or general class performance contact me or your recitation instructor during office hours or by appointment Newton s Three Laws 1IfVis constant then Zqust be zero and if ZFO theanust be constant 2 21 m 3 Force due to object A on object B is always exactly equal in magnitude and always exactly opposite in direction to the force due to object B on object A Some Advice 3Your instincts are often wrong Be careful 3 21 mg is yourfriend Trust what it tells you Inertial Reference Frames 3These principles only apply for observers who are not accelerating a socalled inertial frame 3There are philosophical objections to this concept since it s hard to precisely define an inertial frame except as one where Newton s Laws are valid 3Alternative formulations are beyond the scope of this course you don t need to worry about it Forces you know about so far 3Gravity near Earth s surface FMg points down 3String tension Can be given explicitly or implicitly or found from 2172M 30ne example String breaks if tension is larger than XX 3External forces Can be given explicitly or found from 2172M 3 Normal force Almost always found from 217 ma 3 Problem Solving ToolRevisedFreeBody Checklist 3 Draw a clear diagram of each object 3 Think carefully about all of the forces on each object 3 Think carefully about the angles of the forces 3 Chose an axis put it on your drawing 3 Think carefully about the acceleration and put what you know on your drawing 3 Calculate components EFX max EFy my 3 Solve An Old Friend Component Checklist 3Loop through vectors is there a component 3 Is there an angle factor 3 Is it sine or cosine 3 Is it positive or negative Summary 32Fm 2Fma 2Fmzz 3Actionreaction pairs are an important concept in solving problems but need to be considered very carefully especially the fact that the two forces in the pair act on different objects 3Think carefully about which forces can almost always only be determined using 2F ma 3Typical examples are the normal force and string tension
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