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This 2 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 15 views.
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Date Created: 11/18/15
3 Last Lecture 3More 2D examples gtCircular motion 3 Today 3Newton s Three Laws 3 Important Concepts 3Remember how vectors change 3Remember how vectors add OSeparate external and internal forces 3Think carefully about what object each force acts on Important Reminders 3 Exam 1 is this Friday at 10am 3Material covered is through 2D motion 3 Information and sample problems are posted on the web page Also copies of PRS InClass problems and presentation slides 3 In addition to tutoring sessions recitations and office hours there will be a Questions and Answer session tonight from 79pm 3 Next Mastering Physics due next Monday Newton s First Law QObjects move at constant velocity and remain at rest if they start at rest if they are acted on by no net external force aConstant velocity means both magnitude and direction 3N0 net force doesn t mean no force at all just that whatever forces are present add up to zero OOnIy forces between objects not internal forces count 3This works both ways ifVis constant then 275 must be zero and if 2P0 then Vmust be constant Newton s Second Law gt 213 2 ma 3 Everything else we will do in 801 L is an example or a consequence of this equation 3Forces add as vectors 3The total force points in the direction of the acceleration 3The force and acceleration are related by m a property of the object itself Basically how much stuff is there 3Note distinction between mass and weight Units of Force m 3Acceleratlon IS 2 s 3Use caution not to confuse m the mass a property of an object and m the meter a unit of length 3Mass is in kg kg m 2 S 3 So Force is N 3N is the Newton the short unit for force Newton s Third Law 3The most confusing of them all 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 3The two forces are called an actionreaction pair 3The two forces are equal and opposite in direction but do not add to zero and go away in solving problems because they act of different objects 3t only makes sense to add forces on a single object 3lf you consider AB as a single object then these forces become internal and do drop out 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 Summary 3 Force is related to the change in the velocity vector 3 213 2 me 3The unit of force is the Newton which equals kg m 2 S 3 Actionreaction 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 3These concepts only apply as phrased here in inertial reference frames
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