Student Understanding of Statics Principles.ppt

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1、Student Understanding of Statics Principles,Presented by Brittany Johnson Noyce REU in PER at UW 2011Physics Education Group (PEG) Advisors: Peter Shaffer, Paula Heron, and Lillian McDermott,The Physics Education Group: Prior Research,L. C. McDermott, P. S. Shaffer, and M. D. Somers, “Research as a

2、guide for teaching introductory mechanics: An illustration in the context of the Atwoods machine,” Am. J. Phys. 62 (1), 46-55 (1994). L.C. McDermott, P. S. Shaffer, and P.E.G. U. Wash., “Friction and tension,” in Tutorials in Introductory Physics (2005). L. C. McDermott, P. S. Shaffer, and P.E.G. U.

3、 Wash., “Newtons second and third laws,” in Tutorials in Introductory Physics (2010).,2,Outline of Research,Population: Freshman students (N=86) enrolled in Physics 114A, an algebra-based introductory physics course at UW. Freshman students (N=72) enrolled in Physics 121A, a calculus-based introduct

4、ory physics course at UW. Assessment: Completed 3 multiple choice questions taken from the “Statics Concept Inventory” on a mechanics exam after instruction had been completed ( P. S. Steif, 2005). 1 free body diagram problem 2 static friction problems Analysis: Results were compared with the perfor

5、mance of mechanical engineering students (N=125) entering a sophomore statics course at Carnegie Mellon University before any instruction had taken place (P. S. Steif, 2004).,3,The “Statics Concept Inventory”,4,5 Classes of Questions,Free body diagrams Static equivalence of combinations of forces an

6、d couples Type and direction of loads at connections (including different situations of roller, pin in slot, general pin joint, and pin joint on a two-force member) Limit on the friction force due to equilibrium conditions Equilibrium conditions,Example of a pin in slot connection.,5,An Example: Lim

7、it on the Friction Force,Key Concepts: The possibilities of forces between bodies that are connected to, or contact, one another can be reduced by virtue of the bodies themselves, the geometry of the connection, and/or assumptions on friction. In this case, knowing that stationary contacting bodies

8、remain in static equilibrium requires that the friction force between the bodies be less than N. Anticipated Errors: Failure to recognize that N is the limiting value of the static friction force, and instead consider the friction force to be equivalent to N even though equilibrium is maintained wit

9、h a friction force of lesser magnitude. Presuming the friction force is the difference between the driving force and the slipping limit, N.,6,Limit on Friction Force: Question 1,Two blocks are stacked on top of each other on the floor. The friction coefficient, is 0.2 between all contacting surfaces

10、. (Take this to be both the static and kinetic coefficient of friction). Then, the horizontal 10 N force is applied to the lower block. It is observed that neither block moves.,What is the horizontal component of the force exerted by the floor on the lower block? 4 N 6 N 8 N 10 N 18 N,Correct answer

11、: Balances 10 N and satisfies the friction condition since N = 0.2 x 90 N = 18 N.,7,Results and Analysis of Understanding,Limit on friction force question 1 was administered to two introductory physics courses at UW: Physics 114Aan algebra based course in which N=86 students participated. Physics 12

12、1Aa calculus based course in which N=72 students participated.,8,Limit on Friction Force: Question 2,9,Three blocks are stacked on top of one another on a table. Then the horizontal forces shown are applied.,The friction coefficient, , is 0.5 between all contacting surfaces. (This is both the static

13、 and kinetic coefficient of friction).,It is observed that none of the blocks move. (Stated explicitly in the Physics 121 exam only).,Limit on Friction Force: Question 2,Which of the following diagrams best represents the horizontal component of the force acting on the lower face of the top (20 N) b

14、lock?,Limit on the friction force: the friction force must be less than N to satisfy the friction condition in which equilibrium is maintained. Therefore, the friction force N, and N = 0.5 x 20 N = 10 N.,Correct Answer: Balances 8 N and satisfies the friction condition.,10,Results and Analysis of Un

15、derstanding,Limit on friction force question 2 was also administered to two introductory physics courses at UW: Physics 114Aan algebra based course in which N=86 students participated. Physics 121Aa calculus based course in which N=72 students participated,11,Trends in Student Understanding: How oft

16、en do students employ the same incorrect method for finding the friction force in both questions?,12,Further Trends in Student Understanding,13,Of those students that correctly answered question 1 and incorrectly answered question 2, the most commonly chosen incorrect response to question 2 was choi

17、ce “D,” which was arrived at by balancing the driving forces ( Physics 114A 35 %, Physics 121A 65 %).,Further Curriculum Development and Research,Results may demonstrate a need for greater use of the friction tutorials developed by PEG since known conceptual errors persist. Development of friction t

18、utorials that present more complicated systems. Development of friction tutorials that require analysis of a subsystem of contacting bodies. Continued use of the “Statics Concept Inventory” to determine widespread and tenacious student difficulties.,14,Acknowledgements,Research and Teacher Education

19、 Coordinator Nina Tosti,Physics Ph.D. Students Caroline Auchter Paul Emigh Ryan Hazelton Isaac Leinweber Timothy Major Alexis Olsho Brian Stephanik,The Physics Education Group Faculty Lillian C. McDermott Paula Heron Peter Shaffer (MacKenzie Stetzer, now at U. of Maine),Lecturers, Postdocs, and K-12 Teachers Michael (Chuck) Kralovich Donna Messina Michael (Mick) OByrne David Smith,UW Physics REU 2011 Faculty Subhadeep Gupta Alejandro GraciaAdministrative Coordinator Janine NemereverUndergraduate Students Arman Ballado Emilie Huffman Charlie Fieseler Micah Koller Megan Geen Gina Quan,15,