Physics teaching What contribution can be expected from physics education research?

1. Physics teaching What contribution can be expected from physics education research? Laurence Viennot LSDP, University Denis Diderot (Paris7) laurence.viennot@univ-paris-diderot.fr

2. Attractingstudentstowardsphysics: an urgent need

3. Attracting students towards physics: an irrecductible alternative? The nature of science:distorted? Formalism: a stress to keep hidden? It is theory that feeds and inspire creativity A. Fert 08 What about the value of the internal consistency, conciseness , and predictive power of physical theories? What about the pleasure of reasoning?

4. Suggestions for today … Concerns of physics education research (among others) + a few questions +a concern for coherence + a « good method » ? + … + a concern for coherence and conceptual links Exciting topics Small experiments Ordinary topics Mind rituals!

5. Exciting topicsWhat do the students learn?

6. The merits of new topics • « True » physics, therefore (?) good physics • Prestige of cutting edge topics • View of science as evolutive • …

7. Make new topics accessible to every kind of students? (LV GIREP-EPEC, Opatija 2007) • Make new topics accessible to everybody ? (LV ICPE-Marrakech 2007)

8. Appeal of « new »topics Durban (ICPE 2004) « What physics should we teach ? » • Quantum gravity for undergraduates? R. de Mello Koch • A unit on (...) determinism and chaos for introductory physics students P. Laws • Illustrating quantum entanglement in an elementary context G. Roston et al. • Quantum mechanics for everyone: can it be done with technology? D. Zollman An example:

9. A unit on (...) determinism and chaos for introductory physics studentLaws 04 Just an example… Iterative spreadsheet modeling I= mR2 + 1/2( MR2 )  net =  grav +  damping +  springs + driver .

10. Instructors expected them to be surprised that the state of a chaotic system is unpredictable when the torques acting on it are known. …, we found that the Chaos Unit is both vexing and exciting to our students. What did they learn? Instead,studentsoftencommentedthatLaplaciandeterminismis not feasiblebecause of quantum effects.

11. Teaching « exciting » topics: mission impossible? Certainly not, but a need for thorough reflexion, careful selection of goals and strategiesin order to - provide students with some tools for reasoning in order to • help them go further than being «both vexed and excited » , …knowing their tendencies and needs

12. There ARE some good examples • For students: • Laws 04, Advancing physics (2000; Ogborn & coll.: Imaging), … • Public understanding of science: - Aspect 2000, … More details in Appendix, if some time is left

13. Small experimentsWhat could they learn?

14. A ritual small experiment water cardboard A recent workshop on physics education The experiment of the glass filled with water + cardboard and turned upside down The proposed explanation: Cardboard will support water. If turned around, the cardboard feels atmospheric pressure from below, put into orbit? cardboard but only hydrostatic pressure of say, 10cm of liquid, i.e. 1/100 of atmospheric pressure from above

15. Pressure forces exerted by water:a matter of weight of water (only)? « What is pressing on the balloon that is immersed in the water?… water obviously. When I pushed it into water, it felt the pressure of water. but also the air that is pressing on water z p= p0+gz atmospheric pressure and Marie Curie /I. Chavannes 1907

16. Using simple experiments: more profitably? - providing students with some tools for reasoning  … …knowing common tendencies and needs • « evidence », a notion to analyse carefully: • … avoiding to be misleading ?

17. Method: a large consensus Students should be active Taking into account students’ common ideas An experimental setting Making and justifying some predictions Well specified questions about the situation Debates Searching for a rational explanation

18. Glass on Hand W on G A on G Weight glass negl. Glass Hand on G Water C on W G on W E on W Weight cardboard negl. Cardboard A on C W on C A: the atmosphere G: glass W: water E: the Earth The Earth W on E

19. G+W+C on Hand Or much simpler… A on G+W+C Hand on G+W+C Weight glass negl. Glass +Water E on W+G+C +Cardboard A on C+W+G Weight cardboard negl. The Earth W+G+C on E

20. Hand on G+W+C A different spotlighting Earth on G+W+C

21. Method: a large consensus… …compatible with a wide range of strategies Students should be active Taking into account students’ common ideas An experimental setting Well specified questions about the situation Making andjustifying some predictions Searching for a rational explanation Some debates

22. Colour phenomenaChauvet 1994 • White light Wavelengths … …perceived responses to the received light « third of a spectrum »

23. absorbs absorbs absorbs absorbs absorbs • Pigments absorb a part of the received light and diffuse the remaining light. A pigment Red light Green light Blue light Lum. Rouge Lum. Verte Lum. bleu absorbs

24. absorbs A classic question… • Lit by red light, what colour will the letter V appear? A rule: a green pigment • « Correct » answer: « the letter V appears black » • Common idea: red + green = brown (mixing paints) • Observed colour: brown! (the room is not completely dark+ filter) A common idea is reinforced

25. Changing the questionChauvet 94 • Lit by red light, is the letter V visible? absorbs nearly all… • Expected answer; «  the letter V is hardly visible , because the green pigment absorbs nearly all the light» Which remains true in a real situation

26. From a difficulty that is both technical and conceptual… …to a stress on the absorption of light,renouncing the « all or nothing » approachand even …the colour! A green pigment absorbs nearly all:

27. …a stress on the absorption of light,renouncing the « all or nothing *» approachand even …the colour! Very relevant from the standpoint of physics Opens many opportunities to conduct experiments in a real situation and even…in the open air! * Le matériau le plus noir: 0,045% D.L., Sciences et Avenir March 2008, p23,

28. Method: a large consensus… …compatible with a wide range of strategies Students should be active Taking into account common ideas A particular spotlighting of the content Experimental setting Making and justifying predictions Questions well specified …aiming at conceptuals links much more compatible with everyday life debates Searching for a rational explanation…

29. Ordinary topics and the value of coherence

30. Physics as an internally consistent and unifying description: an attractive idea? If yes, then it is worth considering the risks of inconsistency some possible ways of showing the limited but great power of physics An example with a very ordinary topic …

31. A hot air balloon A typical exercise: • A hot air balloon …a total mass of… • Whatever the temperature of the air in the balloon, its pressure will be the same as the surrounding air. (……….) • …Show that to achieve the lift off…must be heated to about ….° C. pO pO pO pO

32. Archimedes upthrust : a matter of weights Fbasket+… + gMair-inside = gM air-outside-sameV Tin Tout Mair-inside = rair-inside V Mair-outside-sameV = rair-outside V pin = pout= p0 r = Mmol p0/RT An example among MANY others: Giancoli, ex. 37: Physics (6th ed). Prentice Hall F

33. Comm: G. Planinsic, 08/08 An example among MANY others: Giancoli, Physics (6th ed). Prentice Hall • 37. (II) A hot-air balloon achieves its buoyant lift by heating the air inside the balloon, which makes it less dense than the air outside. Suppose the volume of a balloon is and the required lift is 2700 N (rough estimate of the weight of the equipment and passenger). Calculate the temperature of the air inside the balloon which will produce the required lift. Assume that the outside air temperature is 0°C and that air is an ideal gas under these conditions. What factors limit the maximum altitude attainable by this method for a given load? (Neglect variables like wind.) • Solution (can be found in “Instructor Resource Center” CD-ROM, Prentice Hall, 2005) : • (…) The gas inside and outside the balloon is air, and so M is the same for inside and outside. Also, since the balloon is open to the atmosphere, the pressure in the balloon is the same as the pressure outside the balloon. (…)

34. But… Serious consequences pO pO pO « Local » ignores « global » and vice versa... pO g Archimedes, where are you?

35. Dpin= -ringDh Dpout= -routgDh p rin< rout Local OK Top Dh Global and local reconciled Global Archimedes OK pin > pout Dh pin = pout pin> pout Aperture P Viennot 04

36. pO pO pO pO Thank you, you have made me think Students’ reactions • No spontaneous detection (1st year: 15 interviews* + degree: N=32*+16**) (same for 76*+29 T-Teachers) • Guided analysis(1st year: 15 interviews*, degree: 21*+16**) -accessible , -takes time but worth it -raised pleasure Viennot 04*, 06* Mathé Viennot 07** A student: using critical sense: needs to be taught

37. Thinking further?

38. z+Dz z The weight of a gas… only one molecule A particule moving vertically in a motionless box, elastic collisions on the walls The mean force (in time) exerted by this particule on the box equals the weight of the particule  True or false ?

39. An elastic collision … A molecule (m) hits a wall perpendicularly with a velocity v et leaves this wall with velocity -v. • Change in linear momentum of the particule: Dp= -2mv v

40. v = (v+ D v) u u v (-u) Change in linear momentum of the particule at the top of the box Dptop= -2m (v + D v) u D v<0 Change in linear momentum of the particule at the bottom of the box Dpbottom= 2mv u Change …during a « cycle » due to the box (up and down, two collisions) Dpparticule,cycle = -2mDv u

41. Change …during a « cycle »(up and down)due to(two collisions with)the box Dpparticule, cycle= -2mDv u v = (v+ D v) u u v (-u) Free fallDv = -gDtu Mean force exerted on the particule by the box during a cycle(2 Dt where Dt is the duration of free fall) fmean force box-on-particule = Dp/2Dt f mean force box-on-particule= mg u

42. Third law v = (v+ D v) u f mean force box-on-particule= mg u Therefore v (-u) f mean force particule-on-box = -mg u The mean force exerted by the particule on the box is equal to its weight

43. It had to be so The mean position (in time) of the centre of mass of the particule during a cycle is the same for all the cycles A Newtonian balance of forces : f mean force box-on-particule+ ( -mg) u = 0 U f mean force box-on-particule= mg u

44. z Back to the atmosphere … • This reasoning is valid no matter what the value of v. • It applies equally well to the vertical component of any non-vertical particular velocity. • The collisions between particles keep the linear momentum constant. The fact that they can intervene during the period considered does not change the mean force exerted in time by the molecules on the sides or the bottom of the box.

45. z z+Dz z Links between An inhomogeneous slice statics et dynamics individual et collective « it has to be so… » and «because»

46. z+Dz z A few reactions

47. Students’ reactions(3rd year univ., N= 13) First question about a column of atmosphere:Yes 13/13 Then, question about a unique molecule: Yes 1/13

48. z z+dz z Destabilised trainee teachers(first professional year, N=19(sec.)+ 20 (univ.) = 39) YN? Is it true that … The mean force exerted by the particle on the box is equal to its weight? 91812 The molecules, via collisions, exert the same force on the ground as if all the molecules of the column above were pile up, motionless, on the ground . 817 14 A slice of atmosphere … , the force df exerted on it by the air around ... and its weight dP are such that dP + df =0 , with dP=-g(z)dzdS u 20910 The weight of a column of atmosphere equals the force exerted on the ground by this column 2289

49. z+Dz z Students’ and TT’ reactions (3rd year univ., N= 13; trainee univ. teachers, N=20) • Guided analysis (in group, 20mn) -requires an effort, but accessible , -worth the time it takes -raised pleasure - never thought before - I like thinking about things that I never thought about before. (St. 3rd year)

50. Students: more details