A Conceptual Framework for Science Education - The Case Study of Force and Movement

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A conceptual framework for science

education: The case study of force

and movementJohn K. Gilbert

a& Arden Zylbersztajn

a

aUniversity of Surrey, Guildford, UK

Published online: 25 Feb 2007.

To cite this article: John K. Gilbert & Arden Zylbersztajn (1985) A conceptual framework

for science education: The case study of force and movement, European Journal of Science

Education, 7:2, 107-120

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EUR. J. sci. E D U C . , 1985, VOL. 7, N O . 2, 107-120

A conceptual framework for scienceeducation:The case study of force and movementJohn K. Gilbert andArden Zylbersztajn*, University of Surrey, Guildford,UKScience education is presented as the negotiat ion of knowledge between several differentperspect ives: those provided by ' sc ient is ts ' sc ience ' , ' curr icular sc ience ' , ' t eachers 'sc i e n c e ' , ' c h i l d r e n ' s sc i e n c e ' and ' s t u d e n t s ' sc i e n c e ' . A case study based on concepts offorce and m o v e m e n t is used to i l luminate these perspectives, and implications for the cur-ricular presentation andclassroom teaching of the ideas are discussed.

IntroductionThe fact that chi ldren tend to develop their own concept ions about thenature of the physical world has been known for a long t ime. Formalresearch on this topic can be traced back to earlier work of Piaget (1929,1930) in which the clinical interview technique was employed for theinvestigation of chi ldren 's interpretat ions of natural phenomena.O n l y in recent years , however , do research workers in the field ofscience educat ion appear to have realized the full educational implicationsof this form of knowledge. Steadi ly increasing research evidence, accumu-lated from different sources, indicates that these conceptions, in the formof expectations, beliefs and meanings for words , cover a large range ofscience concepts (Gilbert andWatts 1983) . There arealso indications that ,fo r a considerable number of pupi l s , some of these concept ions whichprovide personal unders tanding of the world - are strongly held andresistant to traditional forms of teaching (seeD r i v e r andEasley 1978).Rather than represent ing the discovery of a new p h en o men o n , w h atseems to be emerging from this work is a newinterpretat ion of establishedresearch experience. Instead of being regarded simplistically as pr imi t iveforms of unders tanding , that can be easily disposed of in the process offormal schooling, these alternative views of the world are nowstar t ing tobe seen as personal explanations, which make sense from an individual 'spoin t of view. Therefore, f rom a humanist ic perspect ive, their integri ty iscoming to be granted and respected. The corollary is not that these alter-nat ive concept ions should remain unchal lenged, but that the challengingprocess must be reviewed.

* C u r r e n t a d d r e ss : D e p a r t a m e n t o de E d u c a c a o , CCSA, Universidade Federa l do R N, 59000Nata l R.N., Brazil.

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1 0 8 J. K. GILBERT AND A. ZYLBERSZTAJN

This change of perspective is clearly reflected at the semantic level.References implying a negative connotation, such as 'misconcept ions ' or' m i s u n d e r s t a n d i n g s ' are being replaced. Dr iver and Easley (1978) intro-d u c e d the expression 'a l ternative f rameworks ' , Viennot (1979) talkedabout ' spontaneous reasoning ' , Gi lber t et al. (1982) suggested 'children'sscience ' . All signify pupils ' world views which do not conform with theones accepted officially by school science.T h i s new te rminology can be in terpre ted as signalling a m o v e m e n tt o w a r d s a constructivis t approach to science education, according to whichthe role of individuals in the cons truct ion of their personal knowledgeshould be given special consideration. This implies the acceptance of thefact that pupils do enter teaching-learning s i tuations with already exist ingconceptions which influence the way in which they incorporate into theircognit ive s tructures what they areexpected to learn.

The shif t towards a constructivis t approach has also been supportedby a growing awareness on thep a r t of research workers in science educa-t ion, of the changing perspectives adopted by the phi losophy of science inthe last quar ter of a century. Naive realism, postulating a one- to-onerelationship between theory and reality, assuming scientific knowledge tobe directly derived from sense experiences, has been discarded as anaccount of then a t u r e of scientific knowledge. Thework of Hanson (1958) ,Toulmin (1961) , Kuhn (1962) , Hol ton (1973) andFeyerabend (1975) andothers, stresses the role played by 'world views' in thegeneration of scien-tif ic knowledge.The connect ions be tween a constructivis t approach, modern views inphi losophy of science, and recent developments in science educationresearch, were pointed out by Driver (1979) :

. . . pupils, like scientists, come toscience lessons with some ideas onbeliefs alreadyformulated. These beliefs affect theobservations they make and the inferences theydraw from them. Pupils, like scientists, have construed aview of the world toenablethem to cope with situations. Changing this view is not as simple as giving pupilsadditional experiences or sense data. It also involves helping them to reconstructtheir theories or beliefs, to undergo, if you like, the paradigm shifts which haveoccurred in thehistory ofscience.

A conceptual frameworkThe expression 'children's science ' was suggested in order to descr ibethose views of theworld (composed by beliefs, expectations and meaningsfor words) which do not match those of their scientific counterparts,' scientis ts ' science ' (seeG i l b e r t et al. 1982). In the same paper the expres-sion ' teachers ' science ' was in t roduced to represent the teacher 's view-p o i n t s on ideas, as presented to a g r o u p of pupi ls . Teachers , however ,usually prepare their lessons by using curr icular mater ials , and since aspecific curriculum can be viewed, in itself, as a particular version ofscientific knowledge, the expression 'curr icular science ' can be suggestedto represent this version. With this element included, a more completepic ture of the t ransformations and interactions between different forms of

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A CONCEPTUAL FRAMEWORK FOR SCIENCE EDUCATION 1 0 9

knowledge, in the context of secondary school science, can be articulatedas dep icted in figure 1 (see Zy lbersz tajn 1983).In a first stage, 'scientists' science' (S s) is t ransform ed into 'cu rricularscience' (S C R ) , in a process mediated by the act ion of curriculum plannersand textbook writers. Science curricula , e i ther in their simplest forms(e. g. a textbook) or in their more refined versions (e.g. as an integration ofpr inted mater ia ls , AVA, and labora tory equipment , p lus teacher 's guides)are here conceived of as structures representing versions of scientificknowledge .The second stage of t ransformation occurs when a curriculum isim plem ented by a part icular teacher, concern ed w ith a part icular gro up ofpupils , in a part icular school . I t seems reasonable to assume that teachersinterpret the structure of a curriculum in the l ight of their own conceptualstructures and their perception of the si tuat ions they are involved in.Therefore, what is conveyed by them to their pupils ' teachers ' science '(S T) - can be seen as a result of the interaction between 'teachers' science'and 'curricular science', in a specific context.The third stage of transformation takes place in science classes, whenpupils perceive, interpret and process what is presented to them, construc-ting their own personal meanings from the activities they are asked toperform. I t is in that process that their previous knowledge chi ldren 'sscience' (S C h) - appears to play an important role. Those activities areconceptualized in the framework as the interact ion between 'chi ldren'sscience ' and ' teachers ' science ' , the result of which is named 'students 'science' (S S T). Science teachers naturally aim at achieving a close align-ment between 'students ' science ' and 'curricular science ' , but this is not afrequent outcome of secondary school science classes. Gilbert et al. (1982)identified at least four other outcomes, in which 'children's science'appears as an element of 'students' science', to a greater or lesser extent. .T h e conc eptual framew ork pres ente d offers a simplified p ictu re of acomplex real i ty si tuat ion. Teachers, for instance, may complement theirlessons with information extracted from sources other than curricularmaterials; pupils in their turn may interact direct ly with the textbooks andother sources of information. Nevertheless, even considering these pos-sibilities, i t can still be argued that the framework described representsmajor t ransformations of knowledge occurring in the context of secondaryschool science education. A s such, it provides a dist inct way by m eans of

S s \ curriculum w I S C R \ lessonplanning \ j planning

classroom ( S q T )activities \ /V

Figure 1. The conceptual framework.

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1 1 0 J. K. G I L B E R T AND A. Z Y L BERS Z T AJN

which science education at that level can be conceptualized. It is a waythat stresses the important role played by pupils ' a l ternative conceptions,and is, therefore, compatible with the recent t rend taken by research inscience education.I n the r e m a i nde r of th is paper a topic from secondary school scienceeducat ion is explored from the point of view provided by this conceptualframework. Our intention is to i l lustrate how; by focusing on this topicfrom different perspectives, some educational implicat ions can be hi gh-l ighted. Inpart icular , we in tend toshow how acritical analysis of ' curr icularscience ' can be influenced by a study of ' scientists ' science ' and ' chi ldren 'sscience ' .The topic which wil l be explored can be sum m a r i z e d unde r theheading of 'force and m o v e m e n t ' . Its i m por t a nc e for secondary schoolphysics , and for physics education in general , cannot be over-emphasized,since an unde r s t a ndi ng of the relation between force andmovement , f roman inertial point of view, is basic to the c om pr e he ns i on of N e w t oni a nm e c ha ni c s . On the other hand, as will be seen, the t h e m e has repeatedlybeen explored from the poi n t of view of ' chi ldren 's sc ience ' and the diffi-culties associated with learning it have been identified in several studies. Itis certainly not an exaggerat ion to state that 'force and m o v e m e n t ' is con-sidered as a 'paradigmatic case ' by research workers concerned with al ter-nat ive conceptions andtheir implicat ions for learning.The following sections consist of an overview of the historical devel-

o p m e n t of conceptions relating force and movement ( 'scientists ' science ') ,of a review of research on alternative conceptions about the topic( 'chi ldren's science ') , and of an analysis of some aspects related to thecurricular presentat ion of the topic at secondary school physics level( 'curricular science ') .

Force and movement: scientists' science

A s far as classical mechanics is considered, concept ions concerning therelat ionship between force and m o v e m e n t can be divided historically intot hr e e m a j or g r oups : the 'A r is tote l ian view' , the ' i m pe t us t he or y ' of theM i d d l e A g e s, and the ' inertial view' as expressed in N e w t on ' s t he or y ofm o t i o n . T h i s is a rough general izat ion, f i rst because representat iveworkers within these different groups were not uniform in the i r in terpre-tat ions and, second, because there were outstanding intermediate f igures,l ike Gali leo, whose conceptions represented the t ransi t ion between themedieval impetus theory and the inert ial conception of m ot i on . N e ve r t he -less, the division can be a useful device in helping to conceptualize majorstages in the development of the concept of force, especially in its relationt o m ove m e nt .The Aristotelian View: A ris totle 's ideas concerning m ot ion were par t of abroader perspect ive which can be descr ibed as theA ristote lian two-sp hereuniverse (see K uh n 1977). T hi s concept ion considered a finite and com-pletely full universe limited by a sphere of stars. Themajority of its in te-

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A C O N C E P T U A L F R A M E W O R K F OR S C IE N C E E D U C A T IO N 1 1 1

rior was supposed to be filled with a simple element, the ether, aggregatedin a set of nest ing shells containing the planets. The sphere of stars formedthe outer surface of that aggregate of shells, and the sphere containing themoon (the lowest planet) formed i ts inner surface. The earth rested in thecentre of this universe. The sublunary region was f i l led with the fourA ristotel ian elem en ts: earth, w ater , a ir and fire. A t every poin t of thisuniverse some sort of substance was present . Matter and space were insep-arably l inked, with the result that the very notion of a vacuum was absurd.Motion was considered differently with regard to the celestial andsublunary regions. In the former, which was eternal and changeless,motion was supposed to be perfect , that is , uniform, circular and perpetu-al. Terrestrial or sublunary motion, in i ts turn, was divided into naturaland violent . Natural motion was directed to the 'natural places' of objects.In the case of rocks and earthly materials, that destiny was considered to

be the centre of the univers e. A ccordin g to the A ristotel ian view, a stonefalls naturally towards the earth, not because it is attracted by it , butbecause the earth occupies the centre of the universe. The earth occupiedthis posi t ion because i t was, itself, composed of rocky and earthlym aterials . In the A ristotelian un iverse there was no place for a movingearth, and that restr ict ion was incorporated in the Ptolemaic paradigmwhich dominated ast ronomy unt i l the Copernican revolut ion.A ll m otions w hich were not natural were considered violent in theA ristotel ian framework. In this case, a force was need ed to keep a body

moving against i ts 'natural ' incl inat ion, and the greater the force thegreater the velocity. T h e medievalist E rnest A . M oo dy (see W allace 1981),t ranslated A ristot le 's law of m otion into a m od ern algebraic formulat ion as:

w h e r e V stands for the velocity or speed of motion, P for the inertiveprocess giving the body movement , and Al for the resistance of themedium through which the body passes .A ristot le himself never stated his law of m otion in this concise m ath e-matic form. Rather , he discussed separately the changes of velocity due tochanges in the force producing movement or in the resistance of themedium. I t can be argued, however , tha t the mathemat ica l expression pre-sented conveys the m eaning of A ristot le 's statem ents. T he re are two basicaspects of the A ristotelian physics of m otion , sym bolized in the ex pres-sion, that must be stressed; first , the idea that force and velocity aredirectly associated: for a body to have a velocity a force must be beingex erte d; an d second , the impo ssibility of a void existing in the A ristotelianuniverse, as expressed by the inclusion of the resistance of the medium in

the den om inato r of the equation . T h e imp licat ion is that , in a void, resist-ance must be zero and the velocity would be infinite, which is impossiblesince the motion would be instantaneous. That was the reason used byA ristot le to argue for the imp ossibi l i ty of a void, which w as a fundam entalfeature of his finite and filled universe.This theory of motion explained the movement of bodies lying on asurface quite well , but could only offer a complicated and rather clumsy

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by i ts quanti ty of matter , a concept similar to the concept of momentum inmodern science (Kuhn 1977).Nicole Oresme, one of Buridan 's s tudents , cont inued his master ' swork and actually employed the concept of impetus in order to demon-strate the possibility (although not the necessity) of the earth having adiurnal rotat ion. Oresm e 's cou nter-argu m ents to A r is tot le 's and Ptolemy 'stheories, considered a nearly inertial solution to the problem of an arrowthrown vertically, and were very similar to the ones used later by Galileoto define anti-Copernican 'proofs ' of the immobil i ty to the earth (Kuhn1977). With Buridan and Oresme, terrestrial dynamics started to be usedin cosmological arguments, a movement in the direct ion of a uniquephysics to describe earthly and celestial movement.

By the end of the Fourteenth century ' Impetus dynamics ' hadreplaced 'A ristotelian dyn am ics' and durin g the next two following cen-turies it was taught and used by medieval scientists. Galileo, most certain-ly, was influenced by it (Kuhn 1977, Wallace 1981) and it was Galileo whowas to provide the final and crucial l ink between the Impetus theory andNewtonian mechanics .

Galileo : The role played by Galileo in the development of dynamics is,st i l l today, a controversial matter in modern philosophy and history ofscience (Shapere 1974). E rnst M ach, the influential Nin etee nth centuryGerman posi t ivist philosopher, regarded Gali leo as an empiricist , whomade a sharp break, both in content and methodology (the former asresult of the latter) with the pre-existent tradition. From this point ofview, which nowadays has in Drake (1970) i ts best known supporter ,Galileo formulated originally, and in a form equivalent to Newton's firstlaw, the Principle of Inert ia , thus establishing the equivalence betweenuniform rect i l inear motion and rest .A t the opposi te end of the spect rum , Pierre D uh em , a t the turn of thecentury, argued that practically all the ideas attributed to Galileo hadalready been discovered in the Fourteenth century by the impetus theo-rists. Because of that he was, at best , a propagandist for what had alreadybeen accomplished (Shapere 1974). Other authors, such as Koyre (1978)nearly half a century ago, and more recently Feyerabend (1975) stressedthe rat ionalist and anti-empiricist components of Gali leo's approach to thestudy of nature.The issue is very much an open one, and it can be doubted if a con-census will ever be reached on it . The range of Galileo readings is so greatthat i t can be said that everybody has his own view of Galileo (Cohen andWartofsky 1980). What cannot be denied is that the traditional image ofGalileo as the father of the empirical-inductivist 'scientific method', andindeed the very existence of such a method, has been reconsidered. Mostphilosophers and historians of science today seem to accept that Galileo'stheories were developed, not based, on raw observational results , andoften in spite of the m . A s Ko yre (1978) stated, after po intin g out that m ost

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of the so-cal led Gali leo experiments were in rea l i ty ' thought exper iments ' :'One could say, by applying to Galileo the beliefs of a modern physic is t ,tha t he [Gal i leo] had no confidence in observations which had not beenunified theoretically. 'With regard to the role played by Galileo in the formulat ion of thePrinciple of Inert ia , an intermediate view between those held by M a c ha n d D u h e m s e e m s to be more sensible . In one hand there is st rong evi-dence that Galileo was influenced by ' I m pe t us phys i c s ' ( K uhn 1977,Dijksterhuis 1961). On the other hand, his ' impetus' evolved from thealmost-Parisian view, expressed in his early works like 'De Motu' (circa1590), to a near ly Newtonian perspect ive as expressed in his m o r e m a t u r e'D i a l ogue C onc e r n i ng the Two Chief World Systems' publ ished in 1632.This evaluation was influenced by Gali leo's adherence to C ope r n i c i sm andby his a t t e m pt s to solve the physical problems posed by the new cosmology(Feyerabend 1975; Koyre 1978).T he m a i n pur pose of the ' D i a l o g u e ' was to defuse arguments againstthe idea of a moving ear th , which were presented by the defenders of anear th-centred universe . One of the most ser ious arguments was tha t in amoving ear th , a body released from a certain height would fall non-perpendicularly from the poi n t of release to the ground. Gali leo's solut ionto this problem postulated an independence between the vertical and hor i -zonta l mot ions of the body and a conservation of the horizonta l impetus .A t th is s tage , however , im petus had acquired a new m e a ni ng for Galileo(Koyre 1978). It was no longer the 'emotive force ' causing theobject to m ove ,but mot ion in itself, an idea very close to the m o de r n c onc ept of m o m e n t u m .In .one of his classical ' thought experiments ' in the 'D ia logue ' , Gal i leoi n t r oduc e s the idea of conservation of motion by arguing tha t a ballm ovi ng in a horizontal plane will remain in a state of uniform mot ionunless resisted by external impediments . This mot ion of perpetual ly con-served motion in an idealized frictionless plane represented a sharp depar-ture from the Fourteenth century theor ies . F i rs t of all Gali leo presented itas a case of motion tha t was neither violent nor natural , breaking thereforewith the old A ristotel ian dis t inc t ion: mot ion became a state in itself. Fur-t he r m or e , be i ng a state which is conserved, uni form mot ion was located atthe same ontological level as rest (Koyre 1978). The ontological equiva-lence between uniform motion and rest , as states which tend to be con-served, meant tha t in the case of uniform mot ion need not be explained.U s i ng T oul m i n ' s t e r m i nol ogy , not only rest , but now also uniformm ot i on , be c a m e an ' ideal of natura l order ' , and only what deviated fromthese ideals requ ired an explanat ion (Toulmin 1961) .

A l though inert ia l ideas are i m por t a n t in Gali leo's work, he neverstated a 'Principle of Iner t ia ' as expressed in N e w t on ' s F i r s t Law. M o r e -over, he always made reference to m ot i on in a plane rest ing on the e a r t h ' ssurface and not to motion in unconst ra ined space . This led Koyre (1978)to believe that Galileo's inertia was really circular inertia since, if extendedover the earth 's surface, this plane would become a circular surface. Thisis , however, another aspect disputed by scholars (e.g. Shapere 1974).Whilst some ful ly endorse Koyre 's interpretat ion (Dijksterhuis 1969,Cohen 1977), more tradit ional ones argue against it (Drake 1970) .

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The Newtonian Synthesis: A l th o u gh the first clear statement of the ' P r i n -ciple of Iner t ia ' was m a d e by D es car t es ( K u h n 1977;Drake 1970) , thefinal step towards a fully inertial perspective in mech an i cs was providedb y N e w t o n . The first of his famous three laws of motion , presented asaxioms at the beginning of the 'Pr incipia ' s tates that : 'Every body con-t inues in its state of rest , or of uni form mot ion in a right l ine, unless it iscompelled to change that s tate by forces impressed on it' (Di jks terhuis1961). This axiom is followed by his second law of motion stat ing thepropor t ional i ty between the ' change of m o t i o n ' and the 'motive forcei mp r es s ed ' , and by his axiom stating the equal i ty between act ion and reac-t ion. In contrast to his forerunners , however , Newton s tar ted his work byalmost fully accepting a Copernican universe . By consider ing his threeaxioms on motion wi th the laws of planetary mot ion developed by K ep l er ,he derived the Law of Universal Gravi ta t ion . He was, therefore, able todevelop a quanti tat ive cosmology that proved to be extremely successful .The far-reaching effects of the Newtonian synthesis helped his theoryto overcome the init ial reactions of the Car tes ians (whowould not acceptthe act ion- through-dis tance impl ied by the law of gravi tat ion) and toestablish it as the undisputed research paradigm in mechanics dur ing theE i g h t een t h andNineteenth centur ies . Thedevelopments which took placeduring these two centur ies , for instance, the d ev el o p men t of analyticalmechanics, only reflect the articulation of the paradigm in the K u h n i a nsense (Kuhn 1962) , without making changes in its basic principles .

Force and movement: Children's scienceThe area of mechanics hascertainly been the one in which the majority ofstudies on al ternat ive concept ions have concentrated. Inside this area, therelat ionship between force and m o v e m e n t has been thoroughly exploredand there is convincing evidence to s u p p o r t the statement that schoolch i l d r en , andeven some universi ty students , tend to usepre-Gali l ian ideaswhen analys ing movement .In one s tudy repor ted by W a t t s and Zylbersztajn (1981), a quest ion-naire in a mult ip le-choice-wi th-explanat ion format was used in o r d er toassess the popular i ty of some al ternat ive concept ions related to theconcept of force. One h u n d r e d and twenty-five pupils at the end of thethird year of UK secondary school (age 14 years) from four comprehensiveschools part icipated in the s tudy . Six of the 12 quest ions presented aimedat surveying the association between force and m o v e m e n t , the first threeasking about forces on a stone thrown vert ical ly upwards in the air, andthe other three asking about forces on a cannon bal l in flight from muzzlet o g r o u n d . The responses to these quest ions indicated that about 85% ofthe pupils associated force and m o t i o n . T h e y saw the stone as having aforce upward away from the person 's hand as the s t o n e mo v ed u p w ar d s ;the cannon bal l wasseen to have a force away from the cannon, moving itt h r o u g h the air.




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There is evidence showing that the persuasiveness of this belief isquite general . Replications of the work of Watts and Zylbersztajn (1981)with Portuguese university students showed results similar to the original ,s tudy (Thomaz 1983) . Warren (1971) presented to 178 ( in 1968) and 193(in 1970) science and engineering British university entrants a singleprob lem involving uniform circular m otion of a vehicle, requ ir ing the stu-dents to represent the forces acting on i t . Less than a third of the studentsrepresented the resultant force as being radially inward, and about half ofeach group represented the resul tant force in the forward direct ion,showing an intuitive association between force and direction of movementdespite years of formal instruction in physics.Viennot (1979) reported that several hundred students (mainlyFrench, but also British and Belgian) from the last year of secondaryschool to the third year of university, showed how to apply a l inear rela-

tion between force and velocity when answering a paper and pencil testfocussed on their predictions about the motion of bodies. Not sur-prisingly, this conception was more l ikely to emerge in situations whenintui t ive reasoning was required, for instance, when students had tocompare qualitatively the intensity of the force acting on a body attachedto a spring at the same position, but with different speeds. On the otherhand, students tended to associate force with acceleration (as they havesupposedly been taught) when presented with an equat ion of motion andasked to calculate the force.In another study , A me rican universi ty stud ents were asked to drawthe path which objects would take when constrained by a tube to follow acurvilinear path, a horizontal plane, or when free of the constraint( M cC l o s k ey et al. 1980). Over half of them, including many who hadtaken physics courses, advanced answers showing a belief that , at leastinit ially, the objects will continue to move in a circular curved path. Inter-views conducted after the experiment showed that most of the subjects,who drew curved pathways, held the view that an object forced to travel ina curved path acquires a ' force' or a 'momentum' that causes i t to cont inuein curvi l inear motion for sometime after emerging from the tube. This

' force' or 'momentum' eventual ly dissipates , and the object 's projectorygradual ly becomes st raight . A ccording to the autho rs , those beliefs aresimilar to some versions of the medieval Impetus theory, usually to i tsself-expending version.Clement (1982) presents similar claims based on data obtained fromwrit ten tests and video-taped problem-solving interviews. Eighty-eightper cent of a group of 34 engineering students, which took a diagnostictest at the beginning of their first semester (most of them had high schoolphysics although not college physics), gave incorrect answers when asked

to draw arrows showing the forces on a coin moving upwards. In 90% ofthe cases, the error involved the drawing of a force-arrow pointingupwards . Clement suggested that most s tudents presented concept ionswhich were very similar to those in the Impetus theory. It is interesting tonote that the explanat ions advanced by the universi ty students ofClement 's s tudy, when solving the coin problem, were similar to the onespresented by the third-year pupi ls who part icipated in one of the Watts

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and Zylbersztajn (1981) studies, when solving the equivalent s tone prob-lems.The s tudies presented above support the view that pre-Gali lean ideasabout force andm o v e m e n t are not only prevalent among school children,but also in certain cases do persist even after years of formal exposure tophysics teaching. There is also evidence to suggest that , at least whenprojectile motion (vertical or composite) is considered, the concept ions arecloser to the medieval impetus theories than to the older A ristotel ian con-cept ions .

Force and movement: Curricular scienceCurr icular presenta t ions of this topic vary widely. The differencesbetween an enquiry-oriented spiral approach, which informs NuffieldO-level physics, for instance, and the t radi t ional content -or iented t rans-mission approach of more convent ional textbooks, are more than evident .Never theless , a common logic can be identified in the in t roduct ion of theinertial view of m ot i on , a logic related to the role played by frictionalforces. This logic of presenta t ion can be sum m a r i z e d in the followings e q u e n c e :

1. A force is a ' pu l l ' or a ' push ' . T h i s bu i l ds on the intuitive associ-ation between force and muscular effort which is usually rein-forced during the first years of secondary school ;2. a body at rest will continue at rest if there is not a force actingu p o n it. A ' c om m on- se nse ' ba se d pr opos i t i on ;3. a body in movement wil l stop if there is not an a ppa r e n t net forceacting upon it. A not he r 'c om m o n- se nse ' ba se d pr opos i t i on ; in this

case, however, the ' c o m m o n - s e n s e ' is m i sl e a d i ng;4. bodies in m o v e m e n t are usually acted on by frictional forces.Therefore , they tend to stop; th is happens not because these metany forces acting on the body , but because there are frictionalforces opposing itsm o v e m e n t . T h e r e f o r e :5. a body in motion wil l continue to m o v e in the absence of actingforces, friction included; and6. the effect of a force is to change the speed or the direct ion of

m o v e m e n t .The impl ic i t assumpt ion in this logic of explanation is that , once aware ofthe effect of frictional forces, pupils will easily accept an inertial view ofmotion. However , research on alternative conceptions about force andmovement discussed in the previous sect ion suggests that this is not thecase. For a long t ime teachers and textbooks have started the teaching ofNewton 's laws by stressing the fact that Galileo arrived at the Principle of

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Inertia by (dis)regarding the effects of frictional forces. Pucks, air-tracksand air-tables are familiar to most school labs, but even so non-inertial'children's science' seems to persist . Longford and Zollman (1982), forinstance, comment on the strength and persistence of the motion that aforce must continue to act on an object if i t is to continue in motion evenunder (simulated) fr ict ion-free condit ions.A closer look at the historical d evelo pm ent of scientific views on th erelat ion between force and movement indicates that the t ransi t ion to aninertial view of force included far more than the recognition of the effectof frictional forces. A ristotelians (contrary to wh at m ost curricu lar p rese n-tat ions suggest) and impetus theorists were quite aware of the existence offriction, as already shown in the section on 'scientists' science'. Neverthe-less, they were able to accommodate, at least from a qualitative point ofview, the existence of friction with the need of a force to keep a body in

movement . I t is not unreasonable to suppose that a similar accommoda-tion may occur in the_case of school pupils and even older students.Beyond a simple acknowledgement of the resistance effect of fric-tional forces, the adoption of the inertial view of motion involves a changein the ontology of motion. Uniform motion is given the same ontologicalstatus as rest: both are considered as states tending to be conserved, andtherefore do not need to be explained. In this view, only changes in move-ment need an explanation, and hence the introduction of the modernconcept of force.The main problem in the logic underlying the introduction of theinertial view of motion, as summarized above, is that i t puts ' the cartbefore the horse ' : an explanation of why moving bodies tend to come torest based on friction only fully makes sense within an already-presentinert ial framework. For most children, who are intui t ive impetus theorists ,the problem of fr ict ion may not real ly be a problem, and the simple inven-tion to it does not necessarily lead to a change of perspective. We wouldargue, therefore, that inert ial dynamics is ant i- intui t ive not because peopleare not aware of friction, but because it places uniform motion and rest onthe same ontological level.The logic of presentation challenged here can be seen as reflecting thefact that 'curricular science' is stil l dominated by an empirical-inductivistview on the nature of scientific knowledge (Cawthron and Rowell 1978).The superseded image of Gali leo as the prototype of an empirical-inductivist scientist is prevalent in curricular presentat ions, with sometextbooks conveying the impression that the study of motion started withhim . W he n references to previous ideas are mad e, A ristot le is singled o utin ord er to stress Gali leo's achievem ents. W hile A ristot le is presen ted as aphilosopher whose theories were based on metaphysical speculat ion,

Galileo is presented as a scientist supported by hard empirical data.Impetus Theory is not mentioned at al l , and proper considerat ion is notgiven to the connections between the development of the inertial view ofmotion, and paral lel developments in astronomy. This is despite the l ikel i-hood that Gali leo's views on motion were more l ikely influenced by medi-eval dynamics, and by his commitment to a Copernican universe, thaninduced from experimental results .




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ConclusionOur cr i t ique of the curricular presentat ion of some aspects of the relationbetween force and m o v e m e n t has focused on two different, but related,points . F i rs t , wehave pointed out tha t the logic of presenta t ion is based onassumpt ions which arewarranted nei ther by the history of science, nor byresearch on ' chi ldren 's sc ience ' . Second, we suggested that a supersededview on the na t ur e of scientif ic knowledge supports, and is conveyed by,th is presenta t ion.A n u m b e r of studies had recently addressed the issue of how 'chi ld-ren's science ' should be dealt with in the classroom context if a c ons t r uc -t ivist standpoint is to be assured (Driver and Erickson 1983, Gi lber t andWatts 1983) . Here we would like to indicate that a more careful consider-ation of thehistory and thephi losophy of science could notonly be inst ru-m e nt a l in conveying a more updated view on the na t ur e of scientificknowledge , but also in helping the teaching of some concepts .This las t point is part icularly t rue when paral lels can be dr a w nbetween 'chi ldren 's sc ience ' andconceptions which have, historical ly, con-st i tuted 'scientists ' science ' , as ha ppe ns w i t h the topic considered in thispa pe r . It is, for instance , a serious omission that curricular presentat ionsdo not usual ly ment ion the I m pe t us t he or y of motion developed dur ingt he M i dd l e A ge s, w hi c h is similar to a c om m on pa t t e r n in ' chi ldren 'ssc ience ' . By stressing such similari t ies, 'curricular science ' could persuadeteachers to pay more a t tent ion to their pupils ' a l ternative conceptions. Itcould also help pupils to see the value of the i r const ruct ions , and at thesame t ime, by showing howsimilar ones changed in the course of history,it could help them to reconstrue their own views.

AcknowledgementThe ideas expressed in this paper were developed while the first authorw as a research s tudent at the Inst i tu te of E duc a t i ona l D e ve l opm e nt , Uni-versity of S ur r e y . Wewish to express our t ha nks to the Bri t i sh Counci l fora w a r d i ng him a Technical Co-opera t ion Tra ining Fel lowship and to theU ni ve r s i da de F e de r a l do Rio G r a n d e do Norte , Brazi l , for grant ing himan extended study leave. We are extremely grateful to M a ur e e n P ope andMichael Wat ts for the massive intel lectual support which they have pro-vided for us.

ReferencesCA W TH R O N , E. R. andR O W E LL, J. A. 1978, Epistemology andscience education. Studies in

Science Education, Vol. 5, pp. 31-59.CLE M E N T, J. 1982, Students' preconceptions in introductory mechanics. American Journalof Physics,Vol. 1, No. 50, pp.66-71.C O H E N , B. I. 1977,History and the philosophy for science. TheStructure ofScientificTheories, edited by F. Suppe (University of Illinois Press, Urbana).

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A Conceptual Framework for Science Education - The Case Study of Force and Movement

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