Diapositive 1

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Physics teaching What contribution can be
expected from physics education research?
Laurence Viennot LSDP, University Denis
Diderot (Paris7) laurence.viennot_at_univ-paris-dide
rot.fr
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?Attracting students towards physics an urgent
need
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?Attracting students towards physics an
irrecductible alternative?
The nature of sciencedistorted?
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?
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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!
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Exciting topics What do the students learn?
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The merits of new topics

•  True  physics, therefore (?) good physics
• Prestige of cutting edge topics
• View of science as evolutive

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

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Appeal of  new  topics
An example

• 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

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Just an example

• A unit on (...) determinism and chaos for
  introductory physics student Laws 04

Iterative spreadsheet modeling
I mR2 1/2( MR2 )
? net ? grav ? damping ? springs ? driver
.
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Instructors expected them to be surprised that
the state of a chaotic system is unpredictable
when the torques acting on it are known.
What did they learn?
Instead, students often commented that Laplacian
determinism is not feasible because of quantum
effects.

• , we found that the Chaos Unit is both vexing
  and exciting to our students.

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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

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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

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Small experimentsWhat could they learn?
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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
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Pressure forces exerted by watera 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
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Using simple experiments more profitably?

•  evidence , a notion to analyse carefully
• avoiding to be misleading ?

• - providing students with some tools for
  reasoning
•  
• knowing common tendencies and needs

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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
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W on G
Glass on Hand
A on G
Weight glass negl.
Glass
Hand on G
C on W
Water
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
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GWC on Hand
Or much simpler
A on GWC
Hand on GWC
Weight glass negl.
Glass
Water
E on WGC
Cardboard
A on CWG
Weight cardboard negl.
The Earth
WGC on E
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• A different spotlighting

Hand on GWC
Earth on GWC
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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 and justifying some predictions
Searching for a rational explanation
Some debates
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Colour phenomena Chauvet 1994

• White light

Wavelengths
perceived responses to the received
light  third of a spectrum 
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• Pigments absorb a part of the received light and
  diffuse the remaining light.

Red light Green light Blue light
Lum. Rouge Lum. Verte Lum. bleu

• A pigment

absorbs
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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
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Changing the question Chauvet 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
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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
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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 evenin the open air!
Le matériau le plus noir 0,045 D.L.,
Sciences et Avenir March 2008, p23,
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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
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Ordinary topics and the value of coherence
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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
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A hot air balloon
A typical exercise
pO

• 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 offmust be heated
  to about . C.

pO
pO
pO
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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 p 0
r Mmol p0/RT
An example among MANY others Giancoli, ex. 37
Physics (6th ed). Prentice Hall
F
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An example among MANY others Giancoli, Physics
(6th ed). Prentice Hall
Comm G. Planinsic, 08/08

• 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 0C 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. ()

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Serious consequences
But
pO
pO
pO
 Local  ignores  global  and vice versa...
pO
g
Archimedes, where are you?
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Global and local reconciled
Global Archimedes OK
pin gt pout
Dh
pin pout
pingt pout
Aperture
P
Viennot 04
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Students reactions

• No spontaneous detection
• (1st year 15 interviews degree N3216)
  (same for 7629 T-Teachers)
• Guided analysis (1st year 15 interviews,
  degree 2116)
• -accessible ,
• -takes time but worth it
• -raised pleasure

Viennot 04, 06 Mathé Viennot 07
A student using critical sense needs to be
taught
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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 ?
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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
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Change in linear momentum of the particule at
the top of the box Dptop -2m (v D v)
u D vlt0

• 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
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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 fall Dv -g Dt u
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
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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
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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
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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.

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Links between
An inhomogeneous slice

• statics et dynamics
• individual et collective
•  it has to be so  and because

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A few reactions
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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
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Destabilised trainee teachers (first
professional year, N19(sec.) 20 (univ.) 39)

Y N ?
Is it true that

• The mean force exerted by the particle on the box
  is equal to its weight?

9 18 12
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 .
8 17 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
20 9 10
The weight of a column of atmosphere equals the
force exerted on the ground by this column
22 8 9
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Students and TT reactions (3rd year univ., N
13 trainee univ. teachers, N20)

• 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)
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Students more details
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An experienced teacher, interview

• -P1 It comes down to saying transmitting the
  weight, uhm, by the bottom of the box or moving
  all around the box and exerting actions, pressing
  forces, it comes to the same thing. Why does it
  come down to the same thing uhm????
• (After explanation)
• -P1 Oh yes, its because usually, when we study a
  gas, we neglect weight we do not do it in a
  gravitational field
• We have shown in that box there why the pressure
  was greater than there, we have shown it with g.

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From the gas in a horizontal test tube to an
atmosphere
From the hot air balloon to the single molecule
From macro-global
and macro-local
to nanoscopic
A continuity of mutually consistent viewpoints,
in the frame of Newtonian mechanics
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Ordinary topics, but less common questions
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• a stress on coherence, and on links.

Two lines of action -Many situations, a unique
formalism -A unique situation, different
approaches
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Many situations, a unique formalism

• The harmonic oscillator (60s)
• vN, Poisson, exp-t/t radioactive decay etc
• See Advancing Physics IoP (UK, 2000- Ogborn, in
  particular Imaging) , Grade 12 in France
  (2000)
• Boltzmann factor, Change and Chance
  (Black,Ogborn, 70s), Advancing Physics A2 (2001)
  

• And also dvt (Viennot/Leroy delayed
  signals GIREP sem.2004)

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but also
different viewpoints for a given situation
See also macro-micro (Härtel 93 Chabay-Scherwood
95, ..) macro-meso Borghi et al. 96, Viennot 03,
Besson Viennot 04
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Spotlighting of the taught content precisely
argued
Physics education research what can be expected
After preliminary studies (the content itself,
history of science, students ideas)
Ordinary topics and classic experiments
revisited, In particular, design of non ritual
experiments
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How to teach friction Experiments and
modelsBesson et al. AJP 2007 75 12 1106-1113
One more example the concept of dissipation
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Physics education research what can be expected
New topics same approach
After preliminary studies (the content itself,
history of science, students ideas)
Spotlighting of the taught content precisely
argued () Stress on links
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In general terms, students declare their
appreciation
Limited inquiry (LV)
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Reasons for satisfaction students ranking (1
very high)
29 3rd year univ-students
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Final comments
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• without a strong exigence of consistency,
• dislocated physics a near certainty

Strong concern for consistency and links
- awareness that finding answers to classic
exercises is not enough
means
- thorough analysis of  details  relating to
the physics content
- distance with respect to rituals
A cost in time and effort towards abstraction
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• - Its worth it, of course
• - provided we are taught how to do it
• - Critical sense its the most important
  thing, in my life.
• - Sure, explanations, you shouldnt give them
  thoughtlessly, you made me think, me, even if
  its difficult, its fine to thinkWe learn much
  moreI have learnt a lot.
• - Thank you you have made me think
• Why is it the first time someone tells me this?
• Have you got anything else like that
• A topic which would at first glance be
  unattractive to me if I didnt have to work on
  it. 
• As it began with something that wasnt obvious
  for me, the satisfaction is even greater
  because of all the difficulties I succeed in
  overcoming.

Univ. 1st
Grade 10
Univ. 3rd Mediators-to-be
65

• without a strong exigence of consistency,
• dislocated physics a near certainty

Strong concern for consistency and links
Intellectual satisfaction
A linkage worth exploring further
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• Its worth it

• provided we are taught how to do it

If teachers agree to try .
Good for us, not for them
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Inciting teachers to trywhat can we do?
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The conditions for teachers to hear
commonly thought of as limited to
non-classical activities with relevant ,
exciting , topics ?
Suggestion consider it possible and necessary to
raise intellectual satisfaction, with ordinary
topics as well
.
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Some references

• VIENNOT L. 2003 Teaching physics Kluwer
• BESSON, U. VIENNOT L. 2004. Using models at
  mesoscopic scale in teaching physics two
  experimental interventions on solid friction and
  fluid statics, IJSE, 26 (9), pp1083-1110
• CHAUVET, F. 1996. Teaching Colour  Designing and
  Evaluation of a Sequence, European Journal of
  Teacher Education, 19, (2), pp. 119-134
• VIENNOT L. 2004, ICPE meeting, Delhi
• VIENNOT L. 2006.Teaching rituals and students'
  intellectual satisfaction, Phys. Educ. 41 pp.
  400-408. http//stacks.iop.org/0031-9120/41/400.
• MATHE, S. and VIENNOT, L. 2007, The concern for
  coherence among future science mediators, ESERA
  meeting Malmö.
• LAWS, P. 2005, A unit on (...) determinism and
  chaos for introductory physics students, In What
  physics should we teach? Grayson, D.J. (Durban
  Univ. of South Africa Press), p 198
• VIENNOT L. LEROY J.L. 2004. Doppler and Römer
  what do they have in common? Phys. Educ., vol.
  39, issue 3, pages 273 - 280.
• VIENNOT, L. Le poids des mots, le choc des
  molécules. Bull. de lUDPPC, To be published.

laurence.viennot_at_univ-paris-diderot.fr