Unseen minerals all around us (Ockham's Razor – ABC)
I was listening to a recent episode of 'Ockhams' razor' (ABC's series of short science and technology essays) from 2020 called 'Unseen minerals all around us'. As a radio programme, the audience was likely to be diverse in terms of age, interests, and background knowledge and experiences.
The speaker was Allison Britt, Director of Mineral Resources Advice and Promotion, Geoscience Australia ("Australia's pre-eminent public sector geoscience organisation"), and she was describing the large number of elements used in constructing a modern mobile phone – apparently someone had put a phone in a laboratory blender and analysed the smoothie produced! (Please note: that is not a safe activity for a home science practical.)
Allison Britt, Director of Mineral Resources Advice & Promotion, Geoscience Australia – at a live recording of 'Okham's razor'. (Source: Twitter)
As a science teacher (well, retired – but once a science teacher, always a science teacher at heart at least) I tend to be primed to focus on the ways in which teachers and scientists 'make the unfamiliar familiar', and Britt used an analogy with multiple targets.
The source domain was something familiar from everyday life – seasoning food.
I thought this worked really well, although as a purist (and, as noted here before, something of a pedant) I would have liked the third of her comparisons to refer to a difference that was a matter of degree (e.g., 'taste better' cf. 'work more efficiently'). That said, Britt's formulation worked better as scientific poetry:
So, just like adding salt and pepper to a meal makes it taste better:
putting a little rhenium in a jet engine makes it burn faster and hotter;
putting a little scandium in an aeroplane makes it lighter and stronger;
and putting a little indium in your mobile phone makes the touchscreen work.
Britt, 2021
This was an example of a science communicator making the point of how adding a small, sometimes trace, quantity of a substance can make a substantive difference to properties. I imagine that virtually everyone listening to this would have effortlessly understood the comparison – a key criterion for an effective teaching analogy.
Dampening down COVID? (Image by Iván Tamás from Pixabay)
Analogy in science
Analogy is a common technique used in science and science education. In scientific work analogy may be used as a thinking tool useful for generating hypotheses to explore – "what if X is like Y, then that might mean…". That is, we think we understand system Y, so, if for a moment we imagine that system X may be similar, then by analogy that would mean (for example) that A may be the cause of B, or that if we increase C then we might expect D to decrease… Suggesting analogies has been used as a way of introducing a creative activity into school science (Taber, 2016).
Scientists also sometimes use analogies to explain their ideas and results to other scientists. However, analogies are especially useful in explaining abstract ideas to non-experts, so they are used in the public communication of science by comparing technical topics with more familiar, everyday ('lifeworld') phenomena. In the same way, teachers use analogies as one technique for 'making the unfamiliar familiar' by suggesting that the unfamiliar curriculum focus (the target concept to be taught) is in some ways just like a familiar lifeworld phenomena (the analogue or source concept).
So, I was interested to hear Prof. Andrew Hayward, Professor of Infectious Disease Epidemiology and Inclusion Health Research at UCL (University College London), being interviewed on the radio and suggesting that COVID was like a fire:
"Sometimes I like to think of, you know, COVID as a fire, if we are the fuel, social mixing is the oxygen that allows the fuel to burn, vaccines the water that stops the fuel from burning, and COVID cases are the sparks that spread the fire. So, we are doing well on vaccines, but there's lots of dried wood left."
There's quite a lot going on in that short statement. If Prof. Hayward had stopped at "sometimes I like to think of COVID as a fire" this would have been a simile where it is simply observed that one thing is conceived as being a bit like another.
Simile offers a comparison and leaves the listener or reader to work out the nature of the similarity (whereas metaphor, where one thing is described to be another, an example would be 'COVID is a fire', leaves the audience to even appreciate a comparison is being made). Analogy goes further, as it makes a comparison between two conceptual structures (two systems), such that by mapping across them we can understand how the structure of the unfamiliar is suggested to be like the more familiar structure.
That is, there is a mapping (see the figure below) that is based on pairings across the analogy. Here fire and COVID disease are each treated as systems with components that are structured in a parallel way:
COVID (illness): fire
people: fuel
social mixing: oxygen
vaccines: water
COVID cases: sparks
A graphic representation of Prof. Hayward's use of analogy
A lot of us are like kindling
Moreover, having set up this analogy, we are offered some additional information – we are doing well on vaccines (= there is plenty of water to stop fuel burning), but there is still a lot of dried wood. The listener has to understand that the dry wood refers to fuel, and this maps (in the analogy) onto lots of people who can still become infected.
I suspect most people (science teachers perhaps excepted) listening to this interview will not have even explicitly noticed the nature of the analogy, but rather automatically processed the comparison. They would have understood the message about COVID through the analogy, rather than having to actively analyse the analogy itself.
We can stop the sparks spreading the fire
Professor Hayward was asked about contact tracing and suggested that
"…the key thing is the human discussion with somebody who has COVID to identify who their contacts are and to ask them to isolate as well, and that really stops those sparks getting into the population and really helps to dampen down the fire."
That is, that potential COVID cases (that are like sparks in the fire system) can be prevented from mixing with the wider population (who are like fuel in the fire system) and this will dampen down the fire (the illness in the COVID system). {Note 'dampen down' seems to be a metaphor here rather than a true part of the analogy (in which it is the vaccines that have the effect of 'literally' {analogously} dampening down the fire). Stopping sparks mixing with fuel will limit new areas of combustion starting rather than dampening down the existing fire.}
An argument about contact tracing made using the analogy
Again, most people listening to this would likely have taken on board the intended meaning quite automatically, without having to deliberately analyse this answer – even though the response shifts between the target topics (the COVID disease system) and the analogue (the fire system) – so the sparks (fire system – equivalent to infectious cases) are stopped from getting into the population (COVID system – equivalent to the fuel supply).
This is reminiscent of chemistry teaching which slips back and forth between macroscopic and molecular levels of description – and so where references to, for example, hydrogen could mean the substance or the molecule – and the same word may have a different referent at different points in the same utterance (Taber, 2013). Whether this is problematic depends upon the past experiences of the listener – someone with extensive experience of a domain (probably most of the audience of a serious news magazine programme understand enough about combustion and infection to not have to deliberate on the analogy discussed here) can usually make these shifts automatically without getting confused.
Fire requires…AND…AND…
An analogy can only be effective when the analogue is indeed more familiar to the audience (you cannot make the unfamiliar familiar by comparing an unfamiliar target with an analogue that is also unfamiliar) so the use of the analogy by Professor Hayward assumed some basic knowledge about fire. Indeed it seemed to assume knowledge of the so-called 'fire triangle'.
Three factors are need to initiate/maintain combustion: fire may be stopped by removing one or more of these.
This is the idea that for a fire to commence or continue there need to be three things: something combustible to act as fuel; AND oxygen (or another suitable substance – as when iron filings burn in chlorine – but in usual circumstances it will be oxygen); AND a source of energy sufficient to initiate reaction (as burning is exothermic, once a fire is underway it may generate enough heat to maintain combustion – and sparks may spread the fire to nearby combustible material). To extinguish a fire, one needs to remove at least one of these factors – water can act as a heat sink to decrease the temperature, and may also reduce the contact between the fuel and oxygen. Preventing sparks from transferring hot material that can initiate further sites of combustion (providing energy to more fuel) can also be important.
Unobtrusive pedagogy
The quotes here were part of a short interview with a broadcast journalist and intended for a general public audience. Prof. Hayward introduced and developed his analogy as just sharing a way of thinking, and indeed analogy is such a common device in conversation that it was not obviously marked as a pedagogic technique. However, when we think about how such a device works, and what is expected of the audience to make sense of it, I think it is quite impressive how we can often 'decode' and understand such comparisons without any conscious effort. Providing, of course, that the analogue is indeed familiar, and the mapping across the two conceptual structures can be seen to fit.
Analogies can be used as pedagogic devices to make the unfamiliar familiar' – that is by suggesting that something (the unfamiliar thing being explained) is somehow like something else (that is already familiar), the unfamiliar can start to become familiar. The analogy functions like a bridge between the known and the unknown. (Note: the idea of a bridge is being used as simile there – another device that can be used to help make the unfamiliar familiar.)
For an analogy (or simile) to work, the person being taught or communicated with has to already be familiar with the 'source' that act as an analogue for the 'target' being communicated. (If someone did not know what a bridge was, what it is used for, then it would be no help to them to be told that an analogy can function like one! Indeed it would probably just confuse matters.)
An analogy is based on some mapping of structure between two different systems. For example, at one time a common teaching analogy was that the atom was like a tiny solar system. For that to be useful to a learner, they would need to be more familiar with the solar system than the atom. To be used as an effective teaching analogy, the learner would have to understand the relevant parts of the conceptual structure of the solar system idea that were being mapped across to the atom (perhaps a relatively large central mass, the idea of a number of less massive bodies orbiting in some way, a force between the central and peripheral bodies responsible for the centripetal acceleration of the orbiting bodies…).
A person might easily map across irrelevant aspects of the source to the target, perhaps as all the planets are different then all electrons must be different! This might explain why some students assume the force holding the atom together is gravitational!
In teaching science, it is common to use everyday sources as analogues for scientific ideas. But, of course, it is also possible to use scientific ideas as the source to try to explain other target ideas.
Below I reproduce an extract from a recent publication (Taber & Li, 2001). I developed an analogy between enzymatic catalysis (a scientific concept) and scaffolding of learning (an educational or psychological concept), to use is a chapter I co-wrote with Xinyue Li .
The mapping I had in mind was something like this:
Aspect
Source (Enzymatic catalysis)
Target (Scaffolding)
Process
Chemical reaction
Development of new knowledge/skills
Impediment
Large activation energy – barrier far greater than energy available to reactant species
Large learning demand – gap between current capability and mastery of new knowledge/skill exceeds manageable 'learning quantum'
Intervention
Addition of enzyme
Mediation by 'teacher'
Mechanism
Provides alternative reaction pathway with small energy barriers
Structures learning by modelling activity, and leads learner through small manageable steps
Matching
The enzyme 'fits' the reactant molecule and readily binds
A good scaffold matches the learners' current capacity to progress in learning (in the so-called 'ZPD')
Degrees of freedom
The binding of the enzyme to a substrate 'guides' the subsequent molecular reconfiguration
The scaffolding guides the steps in the learning process taken by the learner
Mapping between two analogous conceptual structures
Scaffolding Learning as Akin to Enzymatic Catalysis
"Metaphors and analogies should always be considered critically, as the aspects that do not map onto the target they are being used to illustrate can often be as salient and as relevant as the aspects that map positively. Given that, and in the spirit of offering a way to imagine scaffolding (rather than an objective description) we suggest it may be useful to think of scaffolding learning as like the enzymatic catalysis of a chemical process in the body (see Figure 3).
Figure 3. Scaffolding learning can be seen as analogous to enzymatic catalysis (b) which facilitates a reaction with a substantive energy barrier (a).
Some chemical reactions are energetically viable (in chemical terms, exothermic) and so in thermodynamic terms, occur spontaneously. However, sometimes even theoretically viable (so spontaneous) reactions occur at such a slow rate that for all practical purposes there is no reaction. For example, imagine a wooden dining table in a room at 293 K (20˚C) with an atmosphere containing about 21% oxygen – a situation found in many people's homes. The combustion of the table is a viable chemical process [1] and indeed the wood will (theoretically) spontaneously burn in the air. Yet, of course, that does not actually happen. Despite being a thermodynamically viable process, the rate is so slow that an observer would die of old age long before seeing the table burst into flames, unless some external agent actively initiated the process. If parents returned home from an evening out to be told by their teenage children that the smouldering dining table caught alight spontaneously, the parents would be advised to suspect that actually this was not strictly true. Although the process would be energetically favourable, there is a large energy barrier to its initiation (cf. Figure 3, top image). Should sufficient energy be provided to ignite the table, then it is likely to continue to burn vigorously, but without such 'initiation energy' it would be inert.
The process of catalysis allows reactions which are energetically favourable, but which would normally occur at a slow or even negligible (and in the case of our wooden table, effectively zero) rate to occur much more quickly – by offering a new reaction pathway that has a much lower energy barrier (such that this is more readily breached by the normal distribution of particles at the ambient temperature).
In living organisms, a class of catalysts known as enzymes, catalyse reactions. Enzymes tend to be specific to particular reactions and very effective catalysts, so reactions akin to the burning of organic materials (as found in our wooden table) can occur as part of metabolism at body temperature. The second image in Figure 3 represents the same chemical reaction as in the top image (note the same start and finish points) reflecting how an enzyme changes the reaction pathway, but not the overall reaction. Two particular features of this graphical metaphor are that the overall process is broken down into a number of discrete steps, and the 'initiation energy' needed to get the process underway is very much smaller.
This is similar to the mediation of learning trough scaffolding, where a task that is currently beyond the capacity of the learner is broken down into a sequence of smaller steps, more manageable 'learning quanta', and the learner is guided along a learning pathway. The parallels go beyond this. Part of the way that an enzyme functions is that the enzyme molecule's shape is extremely well matched to bind to a target reactant molecule (something reflected in the teaching analogy of the 'lock and key' mechanism of enzymatic action: the enzyme and substrate molecules are said to fit together like a lock and key). This is analogous to how effective scaffolding requires a teacher to design a scaffold that fits the learner's current level of development: that is, her current thinking and skills. Once the substrate molecule is bound to the enzyme molecule, this then triggers a specific reconfiguration: just as a good scaffolding tool suggests to the learner a particular perspective on the subject matter.
Moreover, whereas a free substrate molecule could potentially follow a good many different pathways, once it is bound to the enzyme molecule its 'degrees of freedom' are reduced, so there are then significant constraints on which potential changes are still viable. Most organic chemistry carried out in vitro (in laboratory glassware) is inefficient as there are often many 'side reactions' that lead to unintended products, just as students may readily take away very different interpretations from the same teaching, so the yield of desired product can be low. However in vivo reactions (in living cells), being enzyme-catalysed, tend to give high yields.
The process of enzymatic catalysis therefore makes the preferred pathway much 'easier', offers a guide along the intended route, and channels change to rule out alternative pathways. Digital tools that support teaching to meet curricular aims, such as apps intended to be used by learners to support study, therefore need to offer similar affordances (structuring student learning) and constraints (reducing the degrees of freedom to go 'off track'). Clearly this will rely on design features built into the tool. Here we very briefly discuss two examples."
[1] We avoid the term 'reaction' here, as strictly a chemical reaction occurs between specific substances. Wood is a material composed of a wide range of different compounds, and so the combustion of wood is a process encompassing a medley of concurrent reactions.
Cause and effect?: People go to different places because of what they are wearing
Keith S. Taber
Image by anwo00 from Pixabay
Annie was a participant in the Understanding Chemical Bonding project. She was a second year 'A level' student (c.18 years of age) when she was talking to me about atoms and electrons, but I was struck with the way she used the word 'because'.
Technically this conjunction is linked with causality, something of importance in science. To say that X occurred because of Y is to claim that Y was a cause of X.
I wanted to clarify if Annie's use of 'because' in that chemical context actually implied that she was describing what she considered a cause, or whether she was using the word more loosely. To probe this I presented what I considered an obviously inappropriate use of 'because': that football fans following different teams in the same city would go to different matches BECAUSE of the colour of the clothes they wore (i.e., hats and scarves traditionally worn to show support to a particular team).
Because the sky is blue, it makes me cry
I expected Annie to point out that this was not the reason, and so 'because' should not be used – which would have then allowed me to return to her earlier use of 'because' in the context of atoms. However, Annie seemed quite happy with my supposedly 'straw-man' or 'Aunt Sally' example:
So we're talking about what you might call cause and effect, that something is caused by something else. We do a lot of talking about cause and effect in science – "this causes that to happen."
If you think about people in Liverpool, only because this is the first analogy that comes to mind, if you actually go to Liverpool on Saturday [*] and wander round, you'll probably find quite a few people wandering around wearing red, and quite a few people wandering around wearing blue, and sometime after lunch you'll find that all the people wearing red, a lot of the people wearing red, tend to move off to one particular place.[**] And the people wearing blue tend to move to a different sort of place, as though they are repelled, you know, similar colours attracted together.
Uh hm.
Agreed?
Yes.
And we could say therefore, that the reason that some people go towards the Liverpool ground, is because they're wearing red, and the reason some people go towards the Everton ground, is because they're wearing blue. Now would that be a fair description?
Yeah.
And do you agree with the sense of cause and effect there – that people go to watch Liverpool because they're wearing red hats and red scarves? And people go to look at Everton because they're wearing blue hats and blue scarves?
Yes.
So would you say the cause of which football team you go to see, the cause of that, is what clothes you happen to be wearing?
(Pause, c.4s)
Unless you're a rambler. {Laughs}…
No, no, well yes, if you're wearing, you're obviously supporting that colour, so, that team, so so you'd assume, that they were going to watch, the team they favoured.
Right, okay, erm, I'll think of a different example, I think.
Because the world is round, it turns me on
Annie did not seem to 'get' what I had thought would be an obvious flaw in the argument. Fans wear the colours of their team to show support and affiliation; and go to the place where their team is playing: but they do not go to the particular stadium because they happen to be wearing red or blue.
This is linked to the difference between causation and correlation. Often two correlated variables do not have a direct causal relationship, but have a relationship mediated by some other factor.
Height of children in a primary school will be correlated with their grade number (on average, the children in the first year are shorter than those in the second year, who are shorter than…). But children are not organised into grades according to height, and height is not caused by grade. Both are independently related to the child's age.
Colour of football scarves is correlated with destination on match day, but one does not cause the other – rather both colour choice and destination are actually due to something else: affiliation to a club. [***]
I switched to a another example I hoped would be familiar, based on a swimming pool. I though the idea that changing rooms are (usually) designated by gender would make it obvious that where people went to change on leaving the pool correlated to, but was not because of, what they were wearing. Again, however, Annie did not seem to consider it inappropriate to describe this in terms of the the different types of swimming costume causing the behaviour.
If you go to the swimming pool, and watch people swimming, you'll find out that some people when they're swimming at a swimming pool, tend to wear a swimming costume that only covers, the hips basically, and other people either a swimming costume that covers most of the trunk, or two separate parts to it. And if you observe them very closely, which is always a bit suspicious at a swimming pool, you'll notice that when they get out of the pool, they're attracted towards different rooms, these changing rooms…
But all the people who just have the one part of the costume, are attracted towards one room, and the others are attracted towards the other room, the ones with sort of either very long costumes or two part costumes. So is it fair to say that it's caused by what clothes they are wearing, that determines which room they go and get changed in?
Yes.
It is?
(Pause, c.4s)
Yes.
That's the cause of it?
(Pause, c5s)
Yeah. It's also conventional as well.
So in both cases Annie was happy to talk in terms of the clothing causing behaviour. After some further discussion Annie seemed to appreciate the distinction I was making, but even if she did not have a flawed notion of causality, it certainly appeared she have developed non-canonical ways of talking about cause and effect.
Because the wind is high, it blows my mind
Annie was a clever person, and I am sure that the issue here was primarily about use of language rather than an inability to understand causation. However, even if our thinking is not entirely verbal, the major role of verbal language in human thought means that when one does not have the language, one may not have the related explicit concepts.
It is very easy to assume that students, especially those we recognise as capable and having been academically successful, share common 'non-technical' language – but there is plenty of research that suggests that many students do not have a clear appreciation of how such terms are canonically used. These are terms we might think people generally would know, such as adjacent, efficient, maximum, initial, omit, abundant, proportion… (Johnstone & Selepeng, 2001). As always, a useful guide to the teacher is 'never assume'.
* At the time of the interview, it was general practice for most English football league matches to be played at 15.00 on a Saturday.
** One constraint on the scheduling of football matches is that, as far as possible, two local rival ('paired') teams should not play home matches on the same day, to avoid potential clashes between large crowds of rival fans. However, such 'paired clashes', as they are technically called (Kendall et al., 2013), are not always avoided.
*** Of course, this is not a direct cause. A person could support one team, yet choose to wear the colours of another for some reason, but their support for a team usually motivates the choice. Social patterns are messier than natural laws.
Sources cited:
Johnstone, A. H., & Selepeng, D. (2001). A language problem revisited. Chemistry Education: Research & Practice in Europe, 2(1), 19-29.
Kendall G., McCollum B., Cruz F.R.B., McMullan P., While L. (2013) Scheduling English Football Fixtures: Consideration of Two Conflicting Objectives. In: Talbi EG. (eds) Hybrid Metaheuristics. Studies in Computational Intelligence, vol 434. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-30671-6_14
I've just seen* an article in Chemistry: Bulgarian Journal of Science Education describing how students intending to be teachers were introduced to ideas about intermolecular bonding by analogy with attraction between people (Karakaş, 2012). In this analogy nuclei are seen as female and electrons as male, and so sometimes the electrons may take an interest in nuclei other than their own, so to speak: hydrogen bonding is seen as a "form of dipole-dipole interactions, caused by highly electronegative atoms (caused by couples with highly attractive females)", occurring between hydrogen and
"oxygen (couple where the nucleus is Maria Sharapova), fluorine (couple where the nucleus is Kim Kardashian) or nitrogen (couple where the nucleus is Beyonce)" (p.345).
This seems to be a variation on an approach that has been around at least since I started teaching (I remember comparing displacement reactions to interactions between couples at parties), and is clearly meant to be a fun idea, as well as having a motivation in terms of making abstract chemical ideas relevant by comparison with something familiar. The study reported was undertaken in Turkey, and I wondered about the cultural acceptability of this approach these days in different contexts. So Karakaş reports that
"the instructor said in a patriarchal society such as Turkey, the male is supposed to take care of the female. Then the instructor said that basically, the male has to revolve around the female like an electron revolving around a nucleus" (p.343).
I suspect that in many countries it might be considered quite inappropriate to make such a comment about gender roles, at least not without a clear sense of intended satire. More significantly, I wonder how acceptable it is to talk about the relative sexual attractiveness of different people – is that politically correct? Especially if the idea was used with adolescent students, many of whom may well be suffering issues relating to their perceptions of their own attractiveness.
Finally, of course, the basic premise, that sexual orientation matches the principle found with electrical charge – opposite charges attract, similar charges repel – would certainly be suspect in the context where I work (where a current issue of public debate is whether same sex couples should be allowed to marry rather than just register civil partnerships). In some ways these complications are a shame, as the analogy will be seen as fun by many learners, and it certainly is something most learners will relate to. This example reminds us that even if chemistry itself can be seen as largely culture-free, teaching and learning of science always takes place in a cultural context that also influences what can be considered good teaching.
Reference: Karakaş, M. (2012). Teaching Intermolecular Forces with Love Analogy: A Case Study. Chemistry: Bulgarian Journal of Science Education, 21(3), 341-348.
* Previously published at http://people.ds.cam.ac.uk/kst24/science-education-research: 9th May 2015
Amy (Y10) suggested that a circuit was "a thing containing wires and components which electricity can pass through…it has to contain a battery as well". She thought that electricity could pass through "most things".
For Amy "resistance is anything which kind of provides a barrier that, which the current has to pass through, slowing down the current in a circuit", and she thought about this in terms of the analogy with water in pipes: "we've been taught the water tank and pipe running round it… just imagine the water like flowing through a pipe, and obviously like, if the pipe becomes smaller at one point, erm, the water flow has to slow down, and that's meant to represent the resistance of something".
So for Amy, charge flow was impeded by physical barriers effectively blocking its way. She made the logical association with the density of a material, on the basis that a material with densely packed particles would have limited space for the charge to flow:
So electricity would "not very easily" pass through a wooden bench "because wood is quite a dense material and the particles in it are quite closely bonded".
In air, however, the particles were "not as dense as a solid". When asked if that meant that electricity can pass through air quite easily, Amy replied: "yeah, I think so".
Amy's connection between the density of particles and the ease with which charge could flow is a logical one, but unfortunately involves a misunderstanding of how charge flows through materials, i.e., from a canonical scientific perspective, thinking about the charge flowing through gaps between particles is unhelpful here. (So this can be considered an alternative conception.) This seems to be a creative associative learning impediment, where prior learning (here, the spacing of quanticles in different materials) is applied, but in a context beyond its range of application.
Amy was a participant in the Understanding Science project. She was interviewed when she had just started her 'A level' (i.e., college) chemistry, and one of the topics that the course had started with was mass spectrometry. She gave me a very detailed account of what she had been taught, despite both casting doubt on the logic of parts of the account, and of the accuracy of her own recollection (see Amy's account of mass spectrometry *). One of the unconvincing aspects of the new topic seemed to be the way positive ions were produced by bombarding atoms with (negative) electrons – although she had clearly picked up the point.
She reported that her teacher had demonstrated this point with an analogy. She told me that the teacher was using a lot of analogies, and she seemed to find them a little silly, implying that this analogy was not helpful. This particular example involved a board duster and two matchboxes. One matchbox sat on the duster, and was knocked off by the other matchbox being projected at it.
I thought this was quite interesting, as Amy did think the formation of positive ions was counter-intuitive, but had remembered that this is what happened, and seemed to both remember and understand the use of the analogy – even though she was somewhat dismissive of it. I didn't get the chance to explore the issue at the time, but wondered if this was an example of a student maybe not appreciating the role of models and analogies (and simulation) in science itself, and so feeling that using such a device in teaching science was a little 'naff'.
Amy's explanation of the stupid-sounding bit
Amy was dismissive of the teacher's analogical teaching model, even though she seemed to have remembered what he was illustrating:
I mean there was a couple of bits there that you didn't seem too sure about like, like er you know you sort of, you seemed to almost disown the fact that this electron gun is going to make these things into positive ions, you didn't seem very convinced by that?
Erm – I dunno if it's that I'm not convinced it just sounds weird, because it's like erm (pause, c.2s) I dunno, well it's like it's not something which you can see,
No.
and it's like, I dunno, he did this sort of example using a duster and two matchboxes, and, which wasn't very good, so.(Amy was laughing at this point)
Tell me about that then, how does that work? You see I know a bit about this, I don't know about the duster and the matchboxes.
Like no disrespect to our teacher but he uses these analogies, a duster being an atom with matchboxes being the electrons and something, and them being knocked off, because, yeah.
So he threw a matchbox at a duster that had a matchbox and he knocked the matchbox off the duster?
Pretty much.
See, it works for me,
(Amy laughs)
and you've remembered it?
Well, yeah, but – yeah.
…
Erm, So you've got this neutral atom, and you're firing negative electrons at it?
Yeah.
Now if you say that to somebody who doesn't know anything about what's going to happen, what do you think might happen if you fire negative electrons at a neutral atom?, what might you get?
A negative ion.
That's what you'd expect I think, isn't it, … well obviously you are firing negative things at it, so you will get negative. But in fact that's not what seems to happen. So he was trying to explain to you why firing negative things, at something neutral, you might end up with something positive. 'cause that's not obvious and logical, is it?
Yeah.
So if you throw a matchbox at a duster that contains a matchbox, you might knock the match box off?
Yeah (Amy laughs).
There is clearly a 'cultural' difference here, between the interviewer (a science teacher by background) and the interviewee (the learner), in that the interviewer 'got' the use of the demonstration as a pretty neat physical analogy, whereas the student clearly was dismissive. In this case Amy's lack of engagement with the modelling process did not seem to limit her learning, but her attitude demonstrated a lack of awareness of the status and roles of models in science (and in learning science) which has potential to act as a deficiency learning impediment if she cannot see how teaching models and analogies can help form mental models of scientific systems.
