Transcript Diapositive 1 - EUPEN: European Physics education Network

Physics teaching
What contribution can be
expected from physics
education research?
Laurence Viennot
LSDP, University Denis Diderot (Paris7)
[email protected]
Attracting students
towards physics: an urgent
need
Attracting
students towards
physics: an
irrecductible
alternative?
Formalism:
a stress to keep hidden?
The nature of science:
It is theory that feeds and
distorted?
inspire creativity A. Fert 08
What about
the pleasure of reasoning?
What about the value of the
internal consistency,
conciseness , and predictive
power of physical theories?
Suggestions for today …
Concerns of physics
education research
(among others)
Exciting topics
+ a few questions
Small
experiments
+a concern for coherence
+ a « good method » ?
+…
Ordinary topics
+ a concern for coherence
and conceptual links
Mind rituals!
Exciting topics
What do the students learn?
The merits of new topics
• « True » physics, therefore (?) good
physics
• Prestige of cutting edge topics
• View of science as evolutive
• …
• Make new topics accessible to every kind of
students?
(LV GIREP-EPEC, Opatija 2007)
• Make new topics accessible to everybody ?
(LV ICPE-Marrakech 2007)
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
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 +  drive
What did they learn?
Instructors expected them to be surprised that the state of a
chaotic system is unpredictable when the torques acting on
it are known.
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.
Teaching « exciting » topics:
mission impossible?
Certainly not, but a need for
thorough reflexion, careful
selection of goals and strategies
in 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
11
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
Small experiments
What could they learn?
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,
but only hydrostatic pressure of say,
10cm of liquid, i.e. 1/100 of atmospheric
pressure from above
put into
orbit?
cardboard
14
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.
but also the air that is pressing on water
When I pushed it into water, it felt
atmospheric pressure and
the pressure of water.
Marie Curie /I. Chavannes
1907
z
p= p0+gz
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
16
Method: a large
consensus
Students should
be active
Taking into account
students’ common ideas
An experimental
setting
Well specified
questions about
the situation
Debates
Making and
justifying some
predictions
Searching for a
rational explanation
17
Glass on Hand
Weight
glass negl.
Glass
Water
Weight
cardboard
negl.
Cardboard
A on G
W on G
Hand on G
C on W
G on W
E on W
A on C
W on C
A: the atmosphere
G: glass
W: water
E: the Earth
The Earth
W on E
18
G+W+C on Hand
Or much
simpler…
Glass
A on G+W+C
Hand on Weight
glass negl.
G+W+C
+Water
E on
W+G+C
+Cardboard
A on
C+W+G
The Earth
W+G+C on
E
Weight
cardboard
negl.
19
A different spotlighting
Hand
on
G+W+C
Earth
on
G+W+C
20
Method: a large
consensus…
Students should
be active
…compatible with a wide
range of strategies
Taking into account
students’ common ideas
An experimental
setting
Well specified
questions about
the situation
Some
debates
Making and
justifying some
predictions
Searching for a
rational
explanation 21
Colour phenomena
Chauvet 1994
• White light
Wavelengths
…
…perceived
responses to the
received light
« third of a
spectrum »
22
Pigments absorb a part of the received light and
diffuse the remaining light.
Red
Lum. light
Rouge
A pigment
Green
light
Lum. Verte
Blue
Lum. light
bleu
absorbs
absorbs
absorbs
absorbs
absorbs
absorbs
23
A classic question…
• Lit by red light, what
colour will the letter V
appear?
A rule: a green pigment
absorbs
• « 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
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
25
From a difficulty that is both technical and conceptual…
…to a stress on the absorption of light,
renouncing the « all or nothing » approach
and even …the colour!
A green pigment
absorbs
nearly all:
26
…a stress on the absorption of light,
renouncing the « all or nothing *» approach
and 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,
27
Method: a large
consensus…
Students
should be
active
…compatible with a wide
range of strategies
Taking into
account
common ideas
A particular
spotlighting of
the content
Experimental
setting
Questions well
specified
debates
Making and
justifying
predictions
Searching for
a rational
explanation…
…aiming at
conceptuals links
much more
compatible with
everyday life
28
Ordinary topics and the value of
coherence
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 …
A hot air balloon
pO
pO
pO
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
Archimedes upthrust : a matter of weights
Fbasket+… + gMair-inside = gM air-outside-sameV
Tout
Tin
pin = pout = p 0
Mair-inside = air-inside V
Mair-outside-
=
sameV
= air-outside V
Mmol p /RT
0
An example among MANY others: Giancoli,
F
ex. 37: Physics (6th ed). Prentice Hall
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 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.
(…)
But…
pO
pO
Serious consequences
pO
g
pO
« Local » ignores « global »
and vice versa...
Archimedes, where are you?
Global and local reconciled
pin > pout
Global
in< out
Archimedes
OK
h
pin = pout
pin= -ingh
pout= -outgh
p
pin> pout
Aperture
P
Top
Local
OK
Viennot 04
h
p
pO
Students’ reactions
pO
O
p
O
• No spontaneous detection
(1st year: 15 interviews* + degree: N=32*+16**)
(same for 76*+29 T-Teachers)
• Guided analysis (1 year: 15 interviews*, degree:
-accessible ,
-takes time but worth it
-raised pleasure
st
Viennot 04*, 06*
Mathé Viennot 07**
21*+16**)
Thank you, you have
made me think
A student: using critical sense: needs to be taught
Thinking further?
The weight of a gas… only one molecule
A particule
moving vertically in a motionless box,
elastic collisions on the walls
z+z
z
The mean force (in time) exerted by
this particule on the box equals the
weight of the particule
True or false ?
An elastic collision …
A molecule (m) hits a wall
perpendicularly with a velocity v et
leaves this wall with velocity -v.
v
Change in linear momentum of the
particule:
p= -2mv
Change in linear momentum of the particule at
the top of the box
ptop= -2m (v +  v) u
v = (v+  v) u
 v<0
u
v (-u)
Change in linear momentum of the particule at
the bottom of the box
pbottom= 2mv u
Change …during a « cycle » due to the box (up and
down, two collisions)
pparticule,cycle = -2mv u
Change …during a « cycle » (up and down)
v = (v+  v) u
due to (two collisions with) the box
u
pparticule, cycle= -2mv u
Free fall
v = -g t u
v (-u)
Mean force exerted on the particule by the box
during a cycle (2 t where t is the duration of free fall)
fmean force box-on-particule =
p/2t
f mean force box-on-particule = mg u
Third law
v = (v+  v) u
f mean force box-on-particule = mg u
v (-u)
Therefore
f mean force particule-on-box = -mg u
The mean force exerted by the particule on
the box is equal to its weight
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
f mean force box-on-particule = mg u
U
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.
An inhomogeneous slice
z+z
Links between
statics et dynamics
individual et collective
« it has to be so… » and «because»
z
z
z+z
z
A few reactions
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
Destabilised trainee teachers
(first professional year, N=19(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
z
z+d
z
z
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
Students’ and TT’ reactions
z+z
(3rd year univ., N= 13; trainee univ. teachers, N=20)
z
• 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)
Students: more details
N=13, 3rd year univ.
Yes,
ranked 3 or 4
on a scale
1
4
No
Yes
Pleasure?
1
12
9
Worth the time it
takes?
0
13
9
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, it’s 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.
From the hot air balloon to the single molecule
From macro-global and macro-local
to nanoscopic
z+z
z
From the gas
in a horizontal test tube
to an atmosphere
A continuity of mutually consistent viewpoints,
in the frame of Newtonian mechanics
Ordinary topics, but less common questions…
…a stress on coherence, and on links.
Two lines of action
-Many situations, a unique formalism
-A unique situation, different approaches
Many situations, a unique formalism …
• The harmonic oscillator (60s)
• √N, Poisson, exp-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 d=vt
(Viennot/Leroy: delayed signals GIREP sem.2004)
X
t
but also
…different viewpoints for a given situation
p
pO
pO
O p
O
See also
macro-micro (Härtel 93; ChabayScherwood 95, ..)
macro-meso Borghi et al. 96,
Viennot 03, Besson Viennot 04
z
z+z
z+dz
z
z
Physics education research: what
can be expected …
After preliminary studies
(the content itself, history of science, students’ ideas) …
Spotlighting of the taught content: precisely argued
Ordinary topics and classic experiments revisited,
In particular, design of non ritual experiments
One more example: the concept of dissipation
How to teach friction: Experiments and models
Besson et al. AJP 2007 75 12 1106-1113
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
In general terms,
students declare their appreciation …
Limited inquiry (LV)
Reasons for satisfaction: students’ ranking (1: very high)
Ranking 
1 or 2
1,2,3
7 to 10
Concrete, visible, sensitive content
16
21
1
2.69
Students are active
8
15
1
3.15
I have understood everything, it was 11
simple
16
3
3.52
Link with everyday life/ recent
developments
6
14
1
3.46
Surprise
11
16
4
3.92
Beautiful reasoning, coherence, links 14
19
1
3.21
Spectacular phenomena, dream
7
9
6
4.54
No mathematical formalism
2
2
8
5,08
Debate, developing critical sense
7
15
3
3.52
Item 
29 3rd year univ-students
Mean
rank
Final comments
without a strong exigence of consistency,
dislocated physics a near certainty
p
pO
pO
O p
O
Strong
concern for
consistency
and links
means
A cost in time and effort
towards abstraction
- awareness that finding
answers to classic
exercises is not enough
- thorough analysis of
« details » relating to the
physics content
- distance with respect
to rituals
-
It’s worth it, of course
-
…provided we are taught how to do it
-
Critical sense: it’s the most important thing, in my life.
-
Sure, explanations, you shouldn’t give them thoughtlessly,
you made me think, me, even if it’s difficult, it’s fine to
think…We learn much more…I 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
didn’t have to work on it.
p
pO
pO
O p
O
Univ. 1st
Grade 10
-
As it began with something that wasn’t obvious for me, […]
the satisfaction is even greater because of all the difficulties I
p
pO
succeed in overcoming.
pO
O p
O
Univ. 3rd
Mediators-to-be
without a strong exigence of consistency,
dislocated physics a near certainty
p
pO
pO
O p
O
Strong
concern for
consistency
and links
Intellectual
satisfaction
A linkage worth exploring further
• « It’s worth it…
…provided we are
taught how to do it »
If teachers agree to try ….
« Good for us,
not for them »
Inciting teachers to try…
what can we do?
The conditions for teachers to hear…
……
Thank you, you
have made me
think
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
p
pO
pO
O p
X
z+z
O
z
t
….
•
•
•
•
•
•
•
•
•
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
l’UDPPC, To be published.
p
p
p OO
O p
O
X
t
z+z
[email protected]
z