Category: language

Sleep can give us energy

Sleep, like food, can give us a bit more energy

Keith S. Taber

Image by Daniela Dimitrova from Pixabay 

Jim was a participant in the Understanding Science Project. When I was talking to students on that project I would ask them what they were studying in science, rather than ask them about my own agenda of topics. However, I was interested in the extent to which they integrated and linked their science knowledge, so I would from time to time ask if topics they told me about were linked with other topics they had discussed with me. The following extract is taken from the fourth of a sequence of interviews during Jim's first year in secondary school (Y7 in the English school system).

And earlier in the year, you were doing about dissolving sugar. Do you remember that?

Erm, yeah.

Do you think that's got anything to do with the human body?

Erm, we eat sugar.

Mm. True.

Gives us energy…It powers us.

Ah. And why do we need power do you think?

So we can move.

This seemed a reasonable response, but I was intrigued to know if Jim was yet aware of metabolism and how the tissues require a supply of sugar even when there is no obvious activity.

Ah what if you were a lazy person, say you were a very lazy rich person? And you were able to lie in bed all day, watch telly, whatever you like, didn't have to move, didn't have to budge an eyelid, … you're rich, your servants do everything for you? Would you till need energy?

Yes.

Why?

I dunno, 'cause being in bed's tired, tiring.

Is it?

When I'm ill, I stay off for a day, I just feel tired, and like at the end of the day, even more tired than I do when I come to school some times.

Jim's argument failed to allow for the difference in initial conditions

Staying in bed all day and avoiding exercise could indeed make one feel tired, but there seemed something of a confound here (being ill) and I wondered if the reason he stayed in bed on these days might be a factor in feeling even more tired than usual.

So maybe when you are ill, you should come to school, and then you would feel better?

No.

No, it doesn't work like that?

No.

Okay, so why do you think we get tired, when we are just lying, doing absolutely nothing?

Because, it's using a lot of our energy, doing something.

Hm, so even when we are lying at home ill, not doing anything, somehow we are using energy doing something, are we?

Yes.

What might that be, what might we use energy for?

Thinking.

I thought this was a good response, as I was not sure all students of his age would realise that thinking involved energy – although my own conceptualisation was in terms of cellular metabolism, and how thinking depend on transmitting electrical signals along axons and across synapses. I suspected Jim might not have been thinking in such terms.

Do you think it uses energy to think?

(Pause, c.3s)

Probably.

Why do you think that?

Well cause, like, when you haven't got any energy, you can't think, like the same as TV, when it hasn't got any energy, it can't work. So it's a bit like our brains, when we have not got enough energy we feel really tired, and we just want to go to sleep, which can give us more energy, a bit like food.

So Jim here offered an argument about cause and effect- when you haven't got any energy, you can't think. This would certainly be literally true (without any source of energy, no biological functioning would continue, including thinking) although of course Jim had clearly never experienced that absolute situation (as he was still alive to be interviewed), and was presumably referring to experiences of feeling mentally tired and not being able to concentrate.

He offered an analogy, that we are like televisions, in that we do not work without energy. The TV needs to be connected to an electrical supply, and the body needs food (such as sugar, as Jim had suggested) and oxygen. But Jim also used a simile – that sleep was like food. Sleep, like food, according to Jim could give us energy.

So sleeping can give us energy?

Yeah.

How does that work?

Er, it's like putting a battery onto charge, probably, you go to sleep, and then you don't have to do anything, for a little while, and you, then you wake up and you feel – less tired.

Okay so, you think you might need energy to think, because if you have not got any energy, you are very tired, you can't think very well, but somehow if you have a sleep, that might somehow bring the energy back?

Yeah.

So where does that energy come from?

(Pause c.2s)

Erm – dunno.

So here Jim used another analogy, sleeping was like charging a battery. When putting a battery on change, we connect it to a charger, but Jim did not suggest how sleep recharged us, except in that we could rest. When sleeping "you don't have to do anything, for a little while", which might explain a pause in depletion of energy supplies, but would not explain how energy levels were built up again.

[A potentially useful comparison here might have been a television, or a lap top used to watch programmes, with an internal battery, where the there is a buffer between the external supply, and the immediate source for functioning.]

This was an interesting response. At one level it was a deficient answer, as energy is conserved, and Jim's suggestion seemed to require energy to be created or to appear from some unspecified source.

Jim's responses here offered a number of interesting comparisons:

  • sleep is a bit like food in providing energy
  • not having energy and not being able to think is like a TV which cannot work without energy
  • sleeping is like putting a battery on charge

Both science, and science teaching/communication draw a good deal on similes, metaphors and analogies, but they tend to function as interim tools (sources of creative ideas that scientists can then further explore; or means to help someone get a {metaphorical!} foothold on an idea that needs to later be more formally understood).

The idea that sleeping works like recharging a battery could act as an associative learning impediment as there is a flaw in the analogy: putting a battery on charge connects it to an external power source; sleep is incredibility important for various (energy requiring) processes that maintain physical and mental health, and helps us feel rested, but does not in itself source energy. Someone who thought that sleeping works like recharging a battery will not need to wonder how the body accesses energy during sleep as they they seem to have an explanation. (They have access to a pseudo-explanation: sleep restores our energy levels because it is like recharging a battery.)

Jim's discourse reflects what has been called 'the natural attitude' or the 'lifeworld', the way we understand common experiences and talk about them in everyday life. It is common folk knowledge that resting gives you energy (indeed, both exercise and rest are commonly said to give people energy!)

In 'the lifeworld', we run out of energy, we recharge our batteries by resting, and sleep gives us energy. Probably even many science teachers use such expressions when off duty. Each of these notions is strictly incorrect from the scientific perspective. A belief that sleep gives you energy would be an alternative conception, and one that could act as a grounded learning impediment, getting in the way of learning the scientific account.

Yet they each also offer a potential entry point to understanding the scientific accounts. In one respect, Jim has useful 'resources' that can be built on to learn about metabolism, as long as the habitual use of technically incorrect, but common everyday, ways of talking do not act as learning impediments by making it difficult to appreciate how the science teacher is using similar language to express a somewhat different set of ideas.

How plants get their food to grow and make energy

Respiration produces energy, but photosynthesis produces glucose which produces energy

Keith S. Taber

Image by Frauke Riether from Pixabay 

Mandy was a participant in the Understanding Science Project. When I spoke to her in Y10 (i.e. when she was c.14 year old) she told me that photosynthesis was one of the topics she was studying in science. So I asked her about photosynthesis:

So, photosynthesis. If I knew nothing at all about photosynthesis, how would you explain that to me?

It's how plants get their food to grow and – stuff, and make energy

So how do they make their energy, then?

Well, they make glucose, which has energy in it.

How does the energy get in the glucose?

Erm, I don't know.

It's just there is it?

Yeah, it's just stored energy

I was particularly interested to see if Mandy understood about the role of photosynthesis in plant nutrition and energy metabolism.

Why do you think it is called photosynthesis, because that's a kind of complicated name?

Isn't photo, something to do with light, and they use light to – get the energy.

So how do they do that then?

In the plant they've got chlorophyll which absorbs the light, hm, that sort of thing.

What does it do once it absorbs the light?

Erm.

Does that mean it shines brightly?

No, I , erm – I don't know

Mandy explained that the chlorophyll was in the cells, especially in the plant's leaves. But I was not very clear on whether she had a good understanding of photosynthesis in terms of energy.

Do you make your food?

Not the way plants do.

…

So where does the energy come from in your food then?

It's stored energy.

How did it get in to the food? How was it stored there?

Erm.

[c. 2s pause]

I don't know.

At this point it seemed Mandy was not connecting the energy 'in' food either directly or indirectly with photosynthesis.

Okay. What kind of thing do you like to eat?

Erm, pasta.

Do you think there is any energy value in pasta? Any energy stored in the pasta?

Has lots of carbohydrates, which is energy.

…

So do you think there is energy within the carbohydrate then?

Yeah.

Stored energy.

Yeah.

So how do you think that got there, who stored it?

(laughs) I don't know.

Again, the impression was that Mandy was not linking the energy value of food with photosynthesis. The reference to carbohydrates being energy seemed (given the wider context of the interview) to be imprecise use of language, rather than a genuine alternative conception.

So do you go to like the Co-op and buy a packet of pasta. Or mum does I expect?

Yeah.

Yeah. So do you think, sort of, the Co-op are sort of putting energy in the other end, before they send it down to the shop?

No, it comes from 'cause pasta's made from like flour, and that comes from wheat, and then that uses photosynthesis.

Now it seemed that it was quite clear to Mandy that photosynthesis was responsible for the energy stored in the pasta. It was not clear why she had not suggested this before, but it seemed she could make the connection between the food people eat and photosynthesis. Perhaps (it seems quite likely) she had previously been aware of this and it initially did not 'come to mind', and then at some point during this sequences of questions there was a 'bringing to mind' of the link. Alternatively, it may have been a new insight reached when challenged to respond to the interview questions.

So you don't need to photosynthesise to get energy?

No.

No, how do you get your energy then?

We respire.

Is that different then?

Yeah.

So what's respire then, what do you do when you respire?

We use oxygen to, and glucose to release energy.

Do plants respire?

Yes.

So when do you respire, when you are going to go for a run or something, is that when you respire, when you need the energy?

No, you are respiring all the time.

Mandy suggested that plants mainly respire at night because they are photosynthesising during the day. (Read 'Plants mainly respire at night'.)

So is there any relationship do you think between photosynthesis and respiration?

Erm respiration uses oxygen – and glucose and it produces er carbon dioxide and water, whereas photosynthesis uses carbon dioxide and water, and produces oxygen and glucose.

So it's quite a, quite a strong relationship then?

Yeah.

Yeah, and did you say that energy was involved in that somewhere?

Yeah, in respiration, they produce energy.

What about in photosynthesis, does that produce energy?

That produces glucose, which produces the energy.

I see, so there is no energy involved in the photosynthesis equation, but there is in the glucose?

Yeah.

Respiration does not 'produce' energy of course, but if it had the question about whether photosynthesis also produced energy might have been expected to elicit a response about photosynthesis 'using' energy or something similar, to give the kind of symmetry that would be consistent with conservation of energy (a process and its reverse can not both 'produce' energy). 'Produce' energy might have meant 'release' energy in which case it might be expected the reverse process should 'capture' or 'store' it.

Mandy appreciated the relationship between photosynthetic and respiration in terms of substances, but had an asymmetric notion of how energy was involved.

Mandy appeared to be having difficult appreciating the symmetrical arrangement between photosynthesis and respiration because she was not clear how energy was transformed in photosynthesis and respiration. Although she seemed to have the components of the scientific narrative, she did not seem to fully appreciate how the absorption of light was in effect 'capturing' energy that could be 'stored' in glucose till needed. At this stage in her learning she seemed to have grasped quite a lot of the relevant ideas, but not quite integrated them all coherently.

Because they're wearing red…

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

Higher resistance means less current for the same voltage – but how does that relate to the formula?

Image by Gerd Altmann from Pixabay 

The higher resistance is when there is less current flowing around the circuit when you have the same voltage – but how does that relate to the formula?

Adrian was a participant in the Understanding Science Project. When I interviewed him in Y12 when he was studying Advanced level physics he told me that "We have looked at resistance and conductance and the formulas that go with them" and told me that "Resistance is current over, voltage, I think" although he did not think he could remember formulae. He thought that an ohm was the unit that resistance is measured in, which he suggested "comes from ohm's law which is the…formula that gives you resistance".

Two alternative conceptions

There were two apparent alternative conceptions there. One was that 'Resistance is current over voltage', but as Adrian believed that he was not good at remembering formulae, this would be a conception to which he did not have a high level of commitment. Indeed, on another occasion perhaps he would have offered a different relationship between R, I, and V. I felt that if Adrian had a decent feel for the concepts of electrical resistance, current and voltage then he should be able to appreciate that 'resistance is current over voltage' did not reflect the correct relationship. Adrian was not confident about formulae, but with some suitable leading questioning he might be able to think this through. I describe my attempts to offer this 'scaffolding' below.

The other alternative conception was to conflate two things that were conceptually different: the defining equation for resistance (that R=V/I, by definition so must be true) and Ohm's law that suggests for certain materials under certain conditions, V/I will be found to be constant (that is an empirical relationship that is only true in certain cases). (This is discussed in another post: When is V=IR the formula for Ohm’s law?)

So, I then proceeded to ask Adrian how he would explain resistance to a younger person, and he suggested that resistance is how much something is being slowed down or is stopped going round. After we had talked about that for a while, I brought the discussion back to the formula and the relationship between R, V and I.

Linking qualitative understanding of relating concepts and the mathematical formula

As Adrian considered resistance as slowing down or stopping current I thought he might be able to rationalise how a higher resistance would lead to less current for a particular potential difference ('voltage').

Okay. Let’s say we had, erm, two circuits, and they both have resistance and you wanted to get one amp of current to flow through the circuits, and you had a variable power supply.

Okay.

And the first circuit in order to get one (amp) of current to flow through the circuit.

Yes.

You have to adjust the power supply, until you had 10 volts.

Okay.

So it took 10 volts to get one amp to flow through the circuit. And the second (unclear) the circuit, when you got up to 10 volts, (there is) still a lot less than one amp flowing. You can turn it up to 25 volts, and only when it got to 25 volts did you get one amp to flow through the circuit.

Yes, okay.

In mathematical terms, the resistance of the first circuit is (R = V/I = 10/1 =) 10Ω, and the second is (25/1 =) 25Ω, so the second – the one that requires greater potential difference to drive the same current, has more resistance.

Do you think those two circuits would have resistance?

Erm, (pause, three seconds) Probably yeah.

This was not very convincing, as it should have been clear that as an infinite current was not produced there must be some resistance. However, I continued:

Same resistance?

No because they are not the same circuit, but – it would depend what components you had in your circuit, if you had different resistors in your circuit.

Yeah, I've got different resistors in these two circuits.

Then yes each would have a different resistance.

Can you tell me which one had the bigger resistance? Or can’t you tell me?

No, I can’t do that.

You can’t do it?

No I don’t think so. No.

Adrian's first response, that the circuits would 'probably' have resistance, seemed a little lacking in conviction. His subsequent responses suggested that although he knew there was a formula he did not seem to recognise that if different p.d.s were required to give the same current, this must suggest there was different resistance. Rather he argued from a common sense position that different circuits would be likely to have different components which would lead to them having different resistances. This was a weaker argument, as in principle two different circuits could have the same resistance.

We might say Adrian was applying a reasonable heuristic principle: a rule of thumb to use when definite information was not available: if two circuits have different components, then they likely they have different resistance. But this was not a definitive argument. Here, then, Adrian seemed to be applying general practical knowledge of circuits, but he was not displaying a qualitative feel for what resistance in a circuit was about in term of p.d. and current.

I shifted my approach from discussing different voltages needed to produce the same current, to asking about circuits where the same potential difference would lead to different current flowing:

Okay, let me, let me think of doing it a different way. For the same two circuits, erm, but you got one let's say for example it’s got 10 volts across it to get an amp to flow.

Yeah. So yes okay so the power supply is 10 volts.

Yeah. And the other one also set on 10 volts,

Okay.

but we don’t get an amp flow, we only get about point 4 [0.4] of an amp, something like that, to flow.

Yeah, yeah.

Any idea which has got the high resistance now?

The second would have the higher resistance.

Why do you say that?

Because less erm – There’s less current amps flowing around the circuit erm when you have the same voltage being put into each circuit.

Okay?

Yes.

This time Adrian adopted the kind of logic one would hope a physics student would apply. It was possible that this outcome was less about the different format of the two questions, and simply that Adrian had had time to adjust to thinking about how resistance might be linked to current and voltage. [It is also possible too much information was packed close together in the first attempt, challenging Adrian's working memory capacity, whereas the second attempt fed the information in a way Adrian could better manage.]

You seem pretty sure about that, does that make sense to you?

Yes, it makes sense when you put it like that.

Right, but when I had it the other way, the same current through both, and one required 10 volts and one required 25 volts to get the same current.

Yes.

You did not seem to be too convinced about that way of looking at it.

No. I suppose I have just thought about it more.

Having made progress with the fixed p.d. example, I set Adrian another with constant current:

Yes. So if I get you a different example like that then…let’s say we have two different circuits and they both had a tenth of an amp flowing,

Okay. Yes.

and one of them had 1.5 volt power supply

Okay yes.

and the other one had a two volt power supply

Yeah.

but they have both got point one [0.1] of an amp flowing. Which one has got the high resistance?

Currents the same, I would say they have got different voltages, yeah, so erm (pause, c.6s) probably the (pause, c.2s) the second one. Yeah.

Because?

Because there is more voltage being put in, if you like, to the circuit, and you are getting less current flowing in and therefore resistance must be more to stop the rest of that.

Yes?

I think so, yes.

Does that make sense to you?

Yeah.

So this time, having successfully thought through a constant p.d. example, Adrian successfully worked out that a circuit that needed more p.d. to drive a certain level of current had greater resistance (here 2.0/0.1 = 20Ω) than one that needed a smaller p.d. (i.e. 1.5/0.1 = 15Ω). However, his language revealed a lack of fluency in using the concepts of electricity. He referred to voltage being "put in" to the circuits rather than across them. Perhaps more significantly he referred to their being "less current flowing in" where there was the same current in both hypothetical circuits. It would have been more appropriate to think of there being proportionally less current. He also referred to the greater resistance stopping "the rest" of the current, which seemed to reflect his earlier suggestion that resistance is how much something is being slowed down or is stopped going round.

My purpose in offering Adrian hypothetical examples, each a little 'thought experiment', was to see if they allowed him to reconstruct the formula he could not confidently recall. As he had now established that

greater p.d. is needed when resistance is higher (for a fixed current)

and that

less current flows when resistance is higher (for a fixed p.d.)

he might (perhaps should) have been able to recognise that his suggestion that "resistance is current over, voltage" was inconsistent with these relationships.

Okay and how does that relate to the formula you were just telling me before?

Erm, No idea.

No idea?

Erm (pause, c.2s) once you know the resistance of a circuit you can work out, or once you know any of the, two of the components you can work out, the other one, so.

Yeah, providing you know the equation, when you know which way round the equation is.

Yes providing you can remember the equation.

So can you relate the equation to the explanations you have just given me about which would have the higher resistance?

So if something has got a higher resistance, so (pause, c.2s) so the current flowing round it would be – the resistance times the voltage (pause, c.2s) Is that right? No?

Erm, so the current is resistance time voltage? Are you sure?

No.

So Adrian suggested the formula was "the current flowing round it would be the resistance times the voltage", i.e., I = R × V (rather than I = V /R ), which did not reflect the qualitative relationships he had been telling me about. I had one more attempt at leading him through the logic that might have allowed him to deduce the general form of the formula.

Go back to thinking in terms of resistance.

Okay.

So you reckoned you can work out the resistance in terms of the current and the voltage?

Yes, I think.

Okay, now if we keep, if we keep the voltage the same and we get different currents,

Yes.

Which has, Which has got the higher resistance, the one with more current or the one with less current?

Erm (Pause, c.6s) So, so, if they keep the same voltage.

That’s the way we liked it the first time so.

Okay.

Let’s say we have got the same voltage across two circuits.

Yes.

Different amounts of current.

Yes.

Which one’s got the higher resistance? The one with more current or the one with less current?

The one with less current.

So less current means it must be more resistance?

Yes.

Ok, so if we had to have an equation R=.

Yes.

What’s it going to be, do you think?

Erm 

(pause, c.7s)

R=

(pause, c.3s)

I don’t know. It's too hard.

Whether it really was too hard for Adrian, or simply something he lacked confidence to do, or something he found too difficult being put 'on the spot' in an interview, is difficult to say. However it seems fair to suggest that the kind of shift between qualitative relationships and algebraic representation – that is ubiquitous in studying physics at this level – did not come readily to this advanced level physics student.

I had expected my use of leading (Socratic) questioning would provide a 'scaffold' to help Adrian appreciate he had misremembered "resistance is current over, voltage, I think", and was somewhat disappointed that I had failed.

Resistance is how much something is being slowed down

Image by Dimitris Doukas from Pixabay 

"Resistance is how much something is being slowed down or is stopped going round"

Adrian was a participant in the Understanding Science Project. When I interviewed him in Y12 when he was studying Advanced level physics he told me that "We have looked at resistance and conductance and the formulas that go with them". However, when asked about the formula, he suggested, without conviction, that "resistance is current over voltage". So, I asked him how he might go about explaining resistance to a younger student:

We will come back to the formula in a minute then, so let us say you had a younger brother or sister who hasn’t done much physics.

Yes.

And doesn’t do, doesn’t like maths, doesn’t like formulas.

Okay.

So what does it mean though? Why is it important? What’s resistance about?

Erm – I would say it was how much something is being slowed down, or erm how much it is being stopped going round. If it is in electric¬… electricity then it is in a circuit. If it’s in like the wide open range of things it's like erm how resistant is something if you push it? How much force does it give back?

So Adrian was aware of electrical resistance, and also aware of resistance in the context of mechanics.

Oh I see, so, erm if I asked you to push that table over there

Yes.

There might be resistance to that?

Yes.

And that’s different to if we were talking about meters and wires and things?

Yes.

Are they similar in some way?

They have got the same name. {laughs}

Got the same name, okay.

They probably are similar. I've never really thought about it.

So although Adrian associated electrical resistance with 'resistance' in mechanical situations, the similarity between the two types of resistance seemed primarily due to the use of the same linguistic label. This was despite him describing the two forms of resistance in similar terms – "how much something is being slowed down… how much it is being stopped going round" cf. "how resistant is something if you push it".

To a physicist, a property such as resistance should be defined precisely, and therefore preferably mathematically – and so operationally in the sense that there is no ambiguity in how it would be measured. However when students are learning, definitions and formulae may be abstract and have little meaning or connection to experience, so qualitative understanding is important. Students' initial suggestions of what technical terms mean when they first learn about them may be vague and flawed, but if this is linked to a feeling for the concept this may ultimately be a better starting point than a formula which cannot be interpreted meaningfully – as seemed to be the case with Adrian.

Arguably, understanding a relationship in qualitative terms can support later formalising the relationship in mathematical terms, whereas trying to learn a formulae by rote may lead to misremembering and algorithmic application (and so, for example, not noticing when non-feasible results are calculated).

Adrian's suggestion that resistance might be"how resistant is something if you push it? How much force does it give back?" presumably linked to his own experiences of pushing and pulling objects around. However, it seemed to confuse notions of inertia and reaction force (as well as possibly frictional forces). If Adrian were to push with a force of 100N on the wall of a building, a puck on an ice rink, or on a sledge on gravel the reaction force would be 100N in each case (cf. Newton's third law) – although the subjective experience of resistance would be very different in the different situations – as would the outcome on the object pushed.

In these situations it may be difficult for a teacher to know if a vague or confused description reflects conceptual confusion (and/)or limited expression. Yet, students need time and opportunities to be able to explore concepts in their own terms to link the abstract scientific ideas with the 'spontaneous conceptions' they have developed based on their own experiences of acting in the world.

The teacher should offer feedback, and model clear language, but needs to recognise that understanding abstract scientific ideas takes time. After all, Aristotle would be considered to have alternative conceptions of mechanics by comparison with today's science, but Aristotle was clearly highly intelligent and gave the matter a lot of thought!

After this there was extended discussion on the way resistance related to current and voltage, following Arian's comment that resistance is current over voltage. As part of this he was asked about ⚗︎ an example where different voltages were needed in different circuits to allow the same current to flow. ⚗︎ He suggested that the circuit with the higher resistance would be the one where "there is more voltage being put in, if you like, to the circuit, and you are getting less current flowing in, and therefore resistance must be more to stop the rest of that".

Adrian's way of talking about the current in the circuits did not seem to reflect a view of current as driven by a given p.d. across a circuit and limited by a certain resistance, but almost as a fixed potential flow, some of which would be permitted to pass, but some of which would be stopped by the resistance ("how much it is being stopped going round", "resistance … to stop the rest of that"). Yet, as suggested above, it can take time, and opportunities for exploration and discussion, for students' concepts and ways of talking about them to mature towards canonical science.

That Adrian could talk of "more voltage…less current…therefore resistance must be more" seemed promising, although ⚗︎ Adrian could not relate his qualitative description to the mathematical representation of the formula. ⚗︎

The brain thinks: grow more fur

The body senses that it's cold, and the brain thinks how is it going to make the body warmer?

Keith S. Taber

Image by Couleur from Pixabay 

Bert was a participant in the Understanding Science Project. In Y11 he reported that he had been studying about the environment in biology, and done some work on adaptation. he gave a number of examples of how animals were adapted to their environment. One of these examples was the polar bear.

…our homework we did about adapting, like how polar bears adapt to their environments, and camels….

And so a polar bear has adapted to the environment?

Yeah.

So how has a polar bear adapted to the environment?

Erm, things like it has white fur for camouflage so the prey don't see it coming up. Large feet to spread out its weight when it's going over like ice. Yeah, thick fur to keep the body heat insulated.

Bert gave a number of other examples, including dogs that were bred with particular characteristics, although he explained this in terms of inheritance of acquired characteristics: suggesting that dogs that have been taught over and over to retrieve have puppies that automatically have already got that sense. Bert realised that this example was due to the work of human breeders, and took the polar bear as an example of a creature that had adapted to its environment.

Yeah, so how does adaption take place then? You've got a number of examples there, bears and dogs and camels and people. So how does adaption take place?

I don't know. It may have something to do with negative feedback.

That's impressive.

Like you have like, you always get like, you always get feedback, like in the body to release less insulin and stuff like that. So in time people like or whatever, organisms, learn to adapt to that. Because if it happens a lot that makes a feedback then it comes, yeah then they just learn to do that.

Okay. Give me an example of that. I'm trying to link it up in my head.

Okay, like the polar bear, like I don't know. It may have started off just like every other bear, but because it was put in that environment, like all the time the body was telling it to grow more fur and things like that, because it was so cold. So after a while it just adapted to, you know, always having fur instead of, you know, like dogs shed hair in the summer and stuff. But like if it was always then they'd just learn to keep shedding that hair.

So if it was an ordinary bear, not a polar bear, and you stuck it in the Arctic, it would get cold?

Yeah.

But you say the body tells it to grow more fur?

Erm, yeah.

How does that work?

I'm not sure, it just … I don't know. Like, erm, like the body senses that it's cold, it goes to the brain, and the brain thinks, well how is it going to go against that, you know, make the body warmer. And so it kind of, you know, it gives these things.

Is that an example of feedback?

Yes.

So Bert seemed to have notion of (it not the term) homoeostasis, that allowed control of such things as levels of insulin. He recognised thus was based on negative feedback – when some problematic condition was recognised (e.g. being too cold) this would trigger a response (e.g., more insulation)to bring about a countering change.

However, in Bert's model, the mechanism was not automatic. Rather it depended upon conscious deliberation: "the brain thinks, well how is it going to …make the body warmer". Bert thought that this process which initially was based on deliberation then became automatic over many generations.

This seems to assume that bears think in similar terms to humans, that they identify a problem and reason a way through. This might be considered an example of anthropomorphism, something that is very common in student (indeed human) thinking. To what extent it may be reasonable to assign this kind of conscious reasoning to bears is an open question.

However there was a flaws in the process described by Bert that he might have spotted himself. This model suggested that once the bear had become aware of the issue, and the needs to address, it would be able to grow its fur accordingly. That is, as a matter of will. Bert would have been aware that he is able to control some aspects of his body voluntarily (e.g., to raise his arm), but he cannot will his hair to grow at a different rate.

Of course, it may be countered that I am guilty of a kind of anthropomorphism-in-reverse: Bert is not a bear, but rather a human who does not need to control hair growth according to environment. So, just because Bert cannot consciously control his own hair growth, this need not imply the same is true for a bear. However, Bert also used the example of insulin levels, very relevant to humans, and he would presumably be aware that insulin release is controlled in his own body without his conscious intervention.

As often happens in interviewing students (or human conversations more generally) time to reflect on the exchange raises ideas one did not consider at the time, that one would like to be able to to text out by asking further questions. If things that were once deliberate become instinctive over time, then it is not unreasonable in principle to suggest things that are automatic now (adjusting insulin levels to control blood glucose levels) may have once been deliberate.

After all, people can control insulin levels to some extent by choosing to eat a different diet. And indeed people can learn biofeedback relaxation techniques that can have an effect on such variables as blood pressure, and some diabetics have used such techniques to reduce their need for medical insulin. So, did Bert think that people had once consciously controlled insulin levels, but over generations this has become automatic?

In some ways this does not seem a very likely or promising idea – but that is a judgement made from a reasonably high level of science knowledge. It is important to encourage students to use their imaginations and suggest ideas as that is an important aspect of how science woks. Most scientific conjectures are ultimately wrong, but they may still be useful tools for moving science on. In the same way, learners' flawed ideas, if explored carefully, may often be useful tools for learning. At the time of the interview, I felt Bert had not really thought his scheme through. That may well have been so, but there may have been more coherence and reflection behind his comments than I realised at the time.

In ionic bonding, they both want to get full outer shells

Keith S. Taber

Mohammed was a participant in the Understanding Science Project. When interviewed in the first term of his upper secondary (GCSE) science course (in Y10), he told me he had been learning about ionic bonding in one of his science classes. Mohammed had quite a clear idea about ionic bonding, which he described in terms of the interactions of two atoms:

And you said in chemistry you've been doing about electron arrangements [electronic configurations], and ionic bonding.

Yeah.

So what's ionic bonding, then?

Ionic bonding is when, like let's say, a sodium atom and take a chlorine atom, which make salt if they react. What happens is – the sodium atom has one electron on its outer shell, and the chlorine atom has seven, now they both want to get full outer shells, so if I er let's say move the electron from the sodium to the chlorine, then the chlorine would have a full outer shell because it would have eight, and because it's lost that shell the sodium will also have eight.

This account of ionic bonding is a common one, although it is inconsistent with the scientific model. A key problem here is that the driving force for bond formation is seen in terms of atoms wanting to complete their electron shells (the 'full shells explanatory principle'). Mohammed's explanation here uses anthropomorphism, as it treats the individual atoms as though they are alive and sentient, acting to meet their own needs – "they both want to get full outer shells".

When Mohammed was probed, he related a full outer shell to atomic stability (a central feature of the full shells explanatory principle).

Okay. How do you know they want full outer shells?

Because it makes them more stable.

Why does it make them more stable?

(pause, c.1 s)

Erm. (Why do electrons?*) (* sotto voce – apparently said to himself)

(pause, c.2s)

Er, because they don't react as much with other elements if they have a full outer shell.

I see.

They don't react.

There is an interesting contrast here between Mohammed's instant response that full shells "makes them more stable", and the long pause as he thought about why this might be so.

His response reflects something quite common in students' explanations n that a student asked why X is the case may respond by explaining why they think X is the case. (That is, as if an appropriate answer to the question "why is it raining so heavily?" would be "because I got soaked through getting here", i.e. actually responding to the question "how do you know that it is raining heavily?")

Such responses seem to be logically flawed, but of course may be a mis-perception of the question being asked (so the learner is answering the question they thought was asked), or (possibly the case here) substituting a response to a related question as a strategy adopted when aware that one cannot provide a satisfactory response to the actual question posed.

The anthropomorphic aspect of his earlier answer was probed:

How do the atoms know that they need to get a full outer shell, they want to get a full outer shell? Do they know about this stability thing?

Not really.

No?

It's just what happens.

Oh, I see, it's just what happens?

Yeah.

So although Mohammed used an anthropomorphic explanation, it seemed he did not mean this literally. (It may seem strange to suggest a 14 year old might consider atoms alive and sentient, but research suggests this is sometimes so!) This has been described as weak anthropomorphism, where the anthropomorphism is only used as a figure of speech. However, such language can act as a grounded learning impediment because if it becomes habitual it can stand in place of a scientific explanation (thus giving no reason to seek a canonical scientific understanding).

I went on to ask Mohammed about the formation of salt in the process he had described.

Iron is too heavy to completely evaporate

Some molten iron would evaporate but not all of it, 'cause it's not like water and it's more heavy

Keith S. Taber

Sophia was a participant in the Understanding Science Project. In her first interview near the start of Y7, Sophia told me that she had learnt "about the particles…all the things that make – the actual thing, make them a solid, and make them a gas and make them a liquid" (i.e. the states of matter). All solids had particles, including (as examples) ice and an iron clamp stand. There would be the same particles in the ice as the iron.

"because they are a solid, but they can change , 'cause if erm they melted they would be a liquid so they would have different particles in…Well they are still the same particles but they are just changing the way they act".

Sophia's suggestion that particles in ice and the iron were the same types of particles as both were solid seems to be 'carving nature' at the wrong joints – that is in this model the particles in ice and (solid) iron would be of one type, whilst those of water and liquid iron would be of another type (that is she had an alternative ontology). Sophia quickly corrected this, so it is not clear if this reflected some intuitive idea or was just 'a slip of tongue'.

According to Sophia the ice could be melted "with something that's hot, like a candle" but for the iron "you need more heat, 'cause it's more, it's a lot more stronger…because it's got more particles pushed together".

Sophia's explanation suggested a causal path (right-hand side) quite different from a canonical causal path (left-hand side)

Strictly the difference is more about the strength of the interactions between particles, than how many were pushed together – although strong bonding forces would tend (all other factors being equal) to lead to particles being bound more tightly and being closer. We might argue here that Sophia seemed to confuse cause and effect – that a higher density of particles was an effect of strong bonding, which would also mean more energy was needed to overcome that bonding. (However, we should also be aware that when students use 'because' (which formally implies causality) they sometimes mean little more than 'is associated with'.)

If the water obtained from melting ice was heated more "it will evaporate into the sky". However, if the molten iron was heated Sophia thought that "some of it would evaporate but not all of it, 'cause it's not like water and it's more heavy". She thought only "a little" of the iron would evaporate to give iron vapour:

"No, I think that water all of it goes, but other material, other liquids some of it will go, not all of it". The rest "if it's cold enough, it will go back into a solid, but if not it really just stays as a liquid".

Sophia's idea that no matter how much liquid iron was heated it would not completely evaporate so some would remain liquid, which seemed to be linked in her mind to its density, seems to be evidence of an alternative conception. Students may not expect that something as (apparently) inherently solid as iron could evaporate (everyday experience may act as a grounded learning impediment), and so may not readily accept that the basic model of the states of matter and changes of state (i.e., a heated liquid will evaporate or boil) can apply to something like iron. Sophia seemed to have formed a hybrid conception – applying the taught model, but with a modification reflecting the counter-intuitive notion that iron could become a vapour.

Conceptual change can be a slow progress, although hybrid conceptions may be 'stepping stones' towards more scientific understandings. However, when I spoke to Sophia in Y8 she did not seem to have progressed further. [See 'Liquid iron stays a liquid when heated'.]

So who's not a clever little virus then?

The COVID-19 virus is not a clever or sneaky virus (but it is not dumb either) 1

Keith S. Taber

Image by Syaibatul Hamdi from Pixabay 

One of the things I have noticed in recent news reports about the current pandemic is the tendency to justify our susceptibility to the COVID-19 coronavirus by praising the virus. It is an intelligent and sneaky foe, and so we have to outwit it.

But no, it is not. It is a virus. It's a tiny collection of nucleic material packaged in a way that it can get into the cells which contain the chemical resources required for the virus to replicate. It is well suited to this, but there is nothing intelligent about the behaviour. (The virus does not enter the cell to reproduce any more than an ice cube melts to become water; or a hot cup of coffee radiates energy to cool down; or a toddler trips over to graze its knee rather than because gravity acts on it.) The virus is not clever nor sneaky. That would suggest it can adapt its behaviour, after reflecting upon feedback from its interactions with the environment. It cannot. Over generations viruses change – but with a lot of variations that fail to replicate (the thick ones in the family?)

Yet any quick internet search finds references to the claimed intellectual capacities of these deadly foes. Now of course an internet search can find references to virtually anything – but I am referring to sites we might expect to be authoritative, or at least well-informed. And this is not just a matter of a hasty response to the current public health emergency as it is not just COVID 19, but, it seems, viruses generally that are considered intellectually superior.

Those smart little viruses

The site Vaccines Today has a headline in a posting from 2014, that "Viruses are 'smart', so we must be smarter", basing its claims on a lecture by Colin Russell, Royal Society University Research Fellow at Cambridge University. It reports that "Dr Russell says understanding how 'clever' viruses are can help us to outsmart them". (At least there are 'scare quotes' in some of these examples.)

An article from 2002 in an on-line journal has the title "The contest between a clever virus and a facultatively clever host". Now I have moaned about the standard of many new internet journals, but this is the Journal of the Royal Society of Medicine, and the article is in volume 95, so I think it is safe to apply the descriptor 'well-established' to this journal.

A headline in Science news for Students (published by Society for Science & the Public) from 2016 reads "Sneaky! Virus sickens plants, but helps them multiply". I am sure it would not take long to find many other examples. An article in Science refers to a "nasty flu virus".

Sneaky viruses

COVID-19 is a sneaky virus according to a doctor writing in the Annals of Internal Medicine. Quite a few viruses seem to be sneaky – the the human papillomavirus is according to an article in the American Journal of Bioethics. The World Health Organisation considers that a virus that causes swine fever, H1N1, is sneaky according to an article in Systematic Reviews in Pharmacy, something also reported by the BMJ.

There are many references in the literature to clever viruses, such as Epstein‐Barr virus according to a piece in the American Journal of Transplantation. The Hepatitis C virus is clever according to an article in Clinical Therapeutics.

Science communication as making the unfamiliar, familiar

Science communication is a bit like teaching in that the purpose of communication is often to be informative (rather than say, social cohesion, like a lot of everyday conversation {and, by the way,it was another beautiful day here in Cambridgeshire today, blue sky – was it nice where you are?}) and indeed to make the unfamiliar, familiar. Sometimes we can make the unfamiliar familiar by showing people the unfamiliar and pointing it out. 'This is a conical flask'. Often, however, we cannot do that – it is hard to show someone hyperconjugation or hysteresis or a virus specimen. Then we resort to using what is familiar, and employing the usual teacher tricks of metaphor, analogy, simile, modelling, graphics, and so forth. What is familiar to us all is human behaviour, so personification is a common technique. What the virus is doing, we might suggest, is hijacking the cell's biochemical machinery, as if it is a carefully planned criminal operation.

Strong anthropomorphism and dead metaphors

This is fine as far as it goes – that is, if we use such techniques as initial pedagogic steps, as starting points to develop scientific understanding. But often the subsequent stage does not happen. Perhaps that is why there are so many dead metaphors in the language – words introduced as metaphors, which over time have simple come to be take on a new literal meaning. Science does its fair share of borrowing – as with charge (when filling a musket or canon). Dead metaphors are dead (that is metaphorical, of course, they were never actually alive) because we simply fail to notice them as metaphors any more.

There are probably just as many references to 'clever viruses' referring to computer viruses as to microbes – which is interesting as computer viruses were once only viruses metaphorically, but are now accepted as being another type of virus. They have become viruses by custom and practice, and social agreement.

Whoever decided to first refer to the covalent bond in terms of sharing presumably did not mean this in the usual social sense, but the term has stuck. The problem in education (and so, presumably, public communication of science) is that once people think they have an understanding, an explanation that works for them, they will no longer seek a more scientific explanation.

So if the teacher suggests an atom is looking for another electron (a weak form of anthropomorphism, clearly not meant to be taken too seriously – atoms are not entities able to look for anything) then there is a risk that students think they know what is going on, and so never seek any further explanation. Weak anthropomorphism becomes strong anthropomorphism: the atom (or virus) behaves like a person because it has needs and desires just like anyone else.

Image by Tumisu from Pixabay 

Why does it matter?

Perhaps in our current situation this is not that important – the public health emergency is a more urgent issue than the public understanding of the science. But it does matter in the long term. Viruses are not clever – they have evolved over billions of years, and a great many less successful iterations are no longer with us. The reason it matters is because evolution is often not well understood.

As an article in Evolution News and Science Today (a title that surely suggests a serious science periodical about evolution) tells us again that "Viruses are, to all appearances, very clever little machines" and asks "do they give evidence of intelligent design" (that is, rather than Darwinian natural selection, do they show evidence of having an intelligent designer?) After exploring some serious aspects of the science of viruses, the article concludes: "So it seems that viruses are intelligently designed" – that is, a position at odds with the scientific understanding that is virtually a consensus view based on current knowledge. Canonical science suggests that natural processes are able to explain evolution. But these viruses are so clever they must surely have been designed (Borg technology, perhaps?)

This is why I worry when I hear that viruses are these intelligent, deliberate agents that are our foes in some form of biological warfare. It is a dangerous way of thinking. So, I'm concerned when I read, for example, that the cytomegalovirus is not just a clever virus but a very clever virus. Indeed, according to an article in Cell Host & Microbe "CMV is a very clever virus that knows more about the host immune system and cell biology than we do". Hm.

(Read about 'anthropomorphism')

Footnote:

1. The subheading was amended on 4th October 2021, after it was quite rightly pointed out to me that the original version, "COVID-19 is not a clever or sneaky virus (but it is not dumb either)", incorrectly conflated the disease with the virus.

Peter and Patricia Pigeon set up house together

Keith S. Taber

In my work I've spent a lot of time analysing the things learners say about science topics in order to characterise their thinking. Although this work is meant to have an ethnographic feel, and to be ideographic (valuing the thinking of the individual in its own terms), there is always an underlying normative aspect: that is, inevitably there is a question of how well learners' conceptualisations match target curricular knowledge and canonical science. We all have intuitions which are at odd with scientific accounts of the world, and we all develop alternative conceptions – notions which are inconsistent with canonical concepts.

Peter and Patricia started seeing each other at this local fence earlier this year.

Soon passion got too much for them and they (publicly) consummated their relationship on this very fence (some birds have no shame).

It is easier to spot this in others (you think what?!) than it is in ourselves. But occasionally you may reflect on the way you think about a topic and recognise aberrations in your own thinking. One of these examples in my own thinking relates to bird's nests. I know that birds build nests as a place to lay and hatch eggs. Using the ground would be very dangerous due to vulnerability to predators. Simply using branches would be precarious – especially as eggs are hardly best shaped to be balanced on a tree branch. I also know that once the young are fledged have fled the nest, it has outlived its purposes.

They quite liked the area, and decided to look for a place nearby.

Soon they had identified a nice place to build their new home in some nearby ivy.

Yet it was only a few years ago – I think when came across discarded nests in the garden – that I released I have carried around with me since quite young the metaphor that a nest is a bird's home – it is where the bird family lives. Perhaps I made up that idea as a child. More likely I was told that or heard it on a children's programme. If so, perhaps it was not meant to be taken too literally – it was just meant to compare the nest with something that would be familiar to a child. But I think well into adulthood I had this notion of that birds lived in trees – not explicitly, but insidiously in the back of my mind: as if a bird had a home in a tree and that was where it was based – unless and until perhaps it could afford to move upmarket to a better tree!

They decided to do their own build, which involved Peter in the tiring work of going out to get building materials.

Peter set about the serious business of setting up their new dream home.

Peter was quite confident, and would often return which rather large pieces of nesting material.

"Oh, that seems to have got caught up."

Over time Peter started to be more realistic in selecting material he could get through the front door.

Although I was well aware (at one level) that birds do not have permanent family homes to which they return at the end of a hard day's exertions, I also had this nest=home identity at the 'back of my mind' giving the impression that this is how birds live. As humans we take for granted certain kinds of forms of life (perhaps home, work, family, etc.), and these act as default templates for understanding the world. This makes anthropomorphising nature seem quite a natural thing to do.

Peter heading out to work, again.

And getting home with his latest acquisition – landing on his feet.

Watching this process develop was quite entertaining. Peter would spend ages pecking at pieces of plant that were firmly fixed in the ground, ignoring nearby loose material. His early attempts to take material back to the nest were troubled. He would take material that was too large to get through the foliage into the secluded nesting area. He would also fly close to 'home' and then abort as found he could not land with his goods. However, he soon seemed to learn what worked, and developed a technique of first flying onto the fence or the roof the ivy was growing on to, so he would not be flying up to the nesting place from the ground in a single stage.

The sequences below show the pigeon flying out from, and back to, the nest.

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The jumping/diving action is clear in the sequence below:

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The fourth and fifth frames in the sequence below show the 'landing gear' coming into position (reminiscent of a bird of prey taking its prey):

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The landing action is also clear near the end of the sequence below:

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Another take off. catching the first few flaps:

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My favourite sequence – quite extended for my hand-held camera work! – in the 11th frame our pigeon is just entering frame right. But notice a sparrow sitting on top of the foliage to the left. The sparrow has presumably seen/heard the much larger bird comings it way, and in the next frame can be seen to be moving its wings ready to take off. The next three frames have the sparrow heading right as the pigeon moves to the left (the sparrow is a smudge beneath the pigeon's left wing in the third of these frames), and the sparrow appears to have disappeared from view in the next, but must have been obscured by the pigeon as it seen to the right of the next frame. The sequence ends with the pigeon in landing mode.

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A salt grain is a particle (but with more particles inside it)

Keith S. Taber

Sandra was a participant in the Understanding Science Project. When I interviewed Sandra about her science lessons in Y7 she told me "I've done changing state, burning, and we're doing electricity at the moment". She talked about burning as being a chemical change, and when asked for another example told me dissolving was a chemical change, as when salt was dissolved it was not possible to turn it back to give salt grains of the same size. She talk me that is the water was boiled off from salt solution "you'd have the same [amount of salt], but there would just be more particles, but they'd be smaller".

As Sandra had referred to had referred to the salt 'particles' being smaller,(as as she had told me she had been studying 'changing state') I wondered if she had bee taught about the particle model of matter

So the salt's got particles. The salt comes as particles, does it?
Yeah.
Do other things come as particles?
Everything has particles in it.
Everything has particles?
Yeah.
But with salt, you can get larger particles, or smaller particles?
Well, most things. Like it will have like thousands and thousands of particles inside it.
So these are other types of particles, are they?
Mm.

So although Sandra had referred to the smaller salt grains as being "smaller particles", it seemed he was aware that 'particles' could also refer to something other than the visible grains. Everything had particles in. Although salt particles (grains?) could be different sizes, it (any salt grain?) would have a great number ("like thousands and thousands") of particles (not grains – quanticles perhaps) inside it. So it seemed Sandra was aware of the possible ambiguity here, that there were small 'particles' of some materials, but all materials (or, at least, "most things") were made up of a great many 'particles' that were very much smaller.

So if you look at the salt, you can see there's tiny little grains?
Yeah.
But that's not particles then?
Well it sort of is, but you've got more particles inside that.

"It sort of is" could be taken to mean that the grains are 'a kind of particle' in a sense, but clearly not the type of particles that were inside everything. She seemed to appreciate that these were two different types of particle. However, Sandra was not entirely clear about that:

So there's two types are of particles, are there?
I don't know.
Particles within particles?
Yeah.
Something like that, is it?
Yeah.
But everything's got particles has it, even if you can't see them?
Yeah.
So if you dissolved your salt in water, would the water have particles?
Ye:ah.
'cause I've seen water, and I've never seen any particles in the water.
The part¬, you can't actually see particles.
Why not?
Because they're too small.
Things can be too small to see?
Yeah.
Oh amazing. So what can you see when you look at water, then? 'cause you see something, don't you?
You can see – what the particles make up.
Ah, I see, but not the individual particles?
No.

Sandra's understanding here seems quite strong – the particles that are inside everything (quanticles) were too small to be seen, and we could only see "what the particles make up". That is, she, to some extent at least, appreciated the emergence of new properties when very large numbers of particles that were individually too small to see were collected together.

Despite this, Sandra's learning was clearly not helped by the associations of the word 'particle'. Sandra may have been taught about submicroscopic particles outside of direct experience, but she already thought of small visible objects like salt grains as 'particles'. This seems to be quite common – science borrows a familiar term, particle, and uses it to label something unfamiliar.

We can see this as extending the usual everyday range of meaning of 'particle' to also include much smaller examples that cannot be perceived, or perhaps as a scientific metaphor – that quanticles are called particles because they are in some ways like the grains and specks that we usually think of as being very small particles. Either way, the choice of a term with an existing meaning to label something that is in some ways quite similar (small bits of matter) but in other ways very different ('particles' without definite sizes/volumes or actual edges/surfaces) can confuse students. It can act as an associative learning impediment if students transfer the properties of familiar particles to the submicroscopic entities of 'particle' theory.

Dissolving salt is a chemical change as you cannot turn it back

Dissolving salt is a chemical change as you cannot turn it back as it was before

Keith S. Taber

Sandra was a participant in the Understanding Science Project. When I interviewed Sandra about her science lessons in Y7 she told me "I've done changing state, burning, and we're doing electricity at the moment". I asked her about burning:

Well, tell me a bit about burning then. What's burning then?
It's just when something gets set on fire, and turns into ash, or – has a chemical change, whatever.
Has a chemical change: what's a chemical change?
It means something has changed into something else and you can't turn it back.
Oh I see. So burning would be an example of that.
Yeah.

So far this seemed to fit 'target knowledge'. However, Sandra suggested that dissolving would also be a chemical change. Dissolving is not normally considered a chemical change in school science, but a physical change, the distinction is a questionable teaching model. (Chemical change is said to involve bond breaking/making, and of course dissolving a salt does involve breaking up the ionic bonding to form solvent-solute interactions.)

Are there other examples?
Erm – dissolving.
So give me an example of something you might dissolve?
Salt.
Okay, and if you dissolve salt, you can't get it back?
Not really, not as it was before.
No. Can you get it back at all?
Sort of, you can like, erm, make the, boil the water so it turns into gas, and then you have salt, salt, salt on the, left there. Sometimes.
But you think that might not be quite the same as it was before?
No.
No. Different in some way?
Yeah
How might it be different?
Be much smaller.
Oh I see, so do you think you'd have less salt than you started with?
You'd have the same, but there would just be more particles, but they'd be smaller.
Ah, so instead of having quite large grains you might have lots of small grains
Yeah.

So Sandra was clear that one could dissolve salt, and then reclaim the same amount of salt by removing the solvent (water) which from the canonical perspective would mean the change was reversible – a criterion of a physical change.

Yet Sandra also thought that although the amount of salt would be conserved, the salt would be in a different form – it would have different grain size. (Indeed, if the water was boiled off, rather than left to evaporate, it might indeed be produced as very small crystals.)

So, Sandra seemed to have a fairly good understanding of the process, but because of the way she interpreted the criterion of a chemical change, something [salt] has changed into something else [solution] and you can't turn it back [with the same granularity]. Large grains will have changed into small grains – so this would, to Sandra's mind, be a chemical change.

Science teachers deserve a great deal of public appreciation. A teacher can teach something so that a student learns it well – and yet still form an alternative conception – here because of the inherent ambiguity in the ways language is used and understood. Sandra's interpretation – if you start off with large particles and end up with smaller particles then you have not turned it back – was a reasonable interpretation of what she had learnt. (It also transpired there was ambiguity in quite what was meant by particles.)