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Unformatted text preview: Page 1 Physics 207 Lecture 10 Physics 207: Lecture 10, Pg 1 Physics 207, Physics 207, Lecture 10, Oct. 8 Lecture 10, Oct. 8 Agenda c Exam I c Newtons Third Law c Pulleys and tension revisited Assignment: Assignment: c MP Problem Set 4A due Oct. 10,Wednesday, 11:59 PM MP Problem Set 4A due Oct. 10,Wednesday, 11:59 PM c For Wednesday, read Chapter 9 For Wednesday, read Chapter 9 c MP Problem Set 5 (Chapters 8 & 9) available soon MP Problem Set 5 (Chapters 8 & 9) available soon Physics 207: Lecture 10, Pg 2 Exam I results Exam I results c Exams should be returned in your next discussion section c Regrades: Write down, on a separate sheet, what you want regraded and why. c With only 110 scores tallied: Mean: 67.0 Median: 67 Std. Dev.: 14.5 Range: High 97 Low 25 Solution posted later today on http://my.wisc.edu Tentative (only 130 scores) 87-100 A 77- 86 A/B 67- 76 B 57- 66 B/C 40- 56 C 30- 39 D Below 30 F Physics 207: Lecture 10, Pg 3 Newton Newton s Laws s Laws Law 1 : An object subject to no external forces is at rest or moves with a constant velocity if viewed from an inertial reference frame. Law 2 : For any object, F NET = F = m a a Law 3 : Forces occur in pairs: F A , B = - F B , A (For every action there is an equal and opposite reaction.) Read: Force of B on A Physics 207: Lecture 10, Pg 4 Newton Newton s Second Law s Second Law The acceleration of an object is directly proportional to the net force acting upon it. The constant of proportionality is the mass. c This expression is vector expression: F x , F y , F z c Units The metric unit of force is kg m/s 2 = Newtons (N) The English unit of force is Pounds (lb) Physics 207: Lecture 10, Pg 5 Newton Newton s Third Law: s Third Law: If object 1 exerts a force on object 2 ( F 2,1 ) then object 2 exerts an equal and opposite force on object 1 ( F 1,2 ) F 1,2 = - F 2,1 IMPORTANT: Newtons 3 rd law concerns force pairs which act on two different objects (not on the same object) ! For every action there is an equal and opposite reaction Physics 207: Lecture 10, Pg 6 Example (non Example (non-contact) contact) F B,E = - m B g EARTH F E,B = m B g Consider the forces on an object undergoing projectile motion F B,E = - m B g F E,B = m B g Page 2 Physics 207 Lecture 10 Physics 207: Lecture 10, Pg 7 Example Example Consider the following two cases (a falling ball and ball on table), Compare and contrast Free Body Diagram and Action-Reaction Force Pair sketch Physics 207: Lecture 10, Pg 8 Example Example The Free Body Diagram m g m g F B,T = N Ball Falls For Static Situation N = m g Physics 207: Lecture 10, Pg 9 Normal Forces Normal Forces Certain forces act to keep an object in place....
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This note was uploaded on 10/30/2011 for the course PHYS 207 taught by Professor Winnokur during the Spring '06 term at Wisconsin.
- Spring '06