Category: deficiency learning impediment

Some stars are closer than the planets

Stars look so little because they are a long way away, but some stars are closer than the planets

Keith S. Taber

Sophia was a participant in the Understanding Science Project. When I interviewed her in her first year of secondary school (Y7 in the English school system). I asked her about what she remembered about the science she had studied in primary school. She told me about she had studied the topic of space, and had learnt about the nine planets. When I asked her if she could name the planets she produced a list of planets including both the moon and sun: "Pluto, Jupiter, Venus, Uranus, Earth, the Sun, the Moon".

[Read 'The sun is the closest of the eleven planets']

As Sophia thought the sun might be a planet, I asked her what a planet was:

Do you know what a planet is?

Erm, it's like – a round – a sphere, in space, kind of. Though we don't know if people live, animals live there or not.

…If I say someone was going through space, in a spaceship, and they are a long, long way away from earth, they've gone a long way across space, and they came across something in space…And er one of the crew said 'oh that's a planet'. And another one of the crew said 'no, that's not a planet'. And you were in charge, you were the captain. How would you decide who was right, whether that was a planet or not in space?

Er

(pause, c.5s)

I'd look if it was all the things that you thought a planet was.

Good, and what would that be?

If it was round, if it was a bit lumpy, a bit – if it was quite big, not like a little star, well there's no stars that little…

It seemed that Sophia (reasonably) thought stars would be larger than planets, which invited an obvious question, that I assumed would have an almost-as-obvious answer.

Why do they [the stars] look so little?

Because they are a long way away.

Oh, I see. So they are big really?

Yeah.

Okay. What's the difference between a star and a planet then?

A star's made up of different things, but planets – can't – cause you don't really see a planet, so you just see stars quite lot.

That's true, there is lots and lots of stars up there, isn't there? So how can you see the stars and not the planets, do you think?

I think the stars, some stars are closer, maybe, than planets.

There seemed to be something of a contradiction here. Sophia thought that 

  • stars were not as 'little' as planets
  • but they seemed little because they were a long way away.
  • but the stars were easier to see than planets
  • so they might be closer to us than the planets.

Both these arguments are logical enough suggestions (things seem smaller, and may be harder to see, if they are a long way off), but there was a lack of integration of ideas as her two explanations relied on seemingly inconsistent premises (that the stars are "are a long way away" but could be "closer, maybe, than planets").

It seemed that Sophia was not aware, or was not bringing to mind, that stars were self-luminous whereas planets were only seen by reflected light. Lacking (or not considering) that particular piece of information acted as a 'deficiency learning impediment' and led to her explaining why the planets could be more difficult to see by suggesting they might not be as close as some stars.

Not considering luminosity as a criterion also seemed to explain why she was not clear that the (self-luminous) sun was not a planet.

[Read 'The sun is the closest of the eleven planets']

Gases in bottles try to escape; liquids try to take the shape

Keith S. Taber

Bill was a participant in the Understanding Science Project. Bill, a year 7 (Y7) student, told me that:

"Gases, they try and fill whole room, they don't, like liquids, they stay at the bottom of the container, but gases go fill, do everywhere and fill, try and fill the whole thing." 

When asked "Why do they try and do that?" he replied that "Erm, I'm not sure." I suggested some things that Bill might 'try' to do, and asked "so when the gas tries to fill the room, is it the same sort of thing, do we mean the same sort of thing by the word 'try'?" Bill appreciated the difference, and recanted the use of 'try':

"No, I think I phrased that wrong, I meant that it fills the whole area, 'cause it can expand."

However, it soon became clear that Bill's use of the term came easily, despite accepting that it was misleading:

Okay. So it's not, the gas does not come in and say, 'hm, I think I'll fill the whole room', and try and do it?

No, it just does it.

It just does it?

It tries to get out of everywhere, so if you put it in the bottle, it would be trying to get out.

And later:

…are there particles in other things?:

liquids, yeah there is particles in everything, but liquids the particles move quite a lot because, well they have, oh we did this this [in the most recent] lesson, erm, they have energy to move, so they try and move away, but their particles are quite close together.

What about the gases?

The gases, their particles try to stay as far away from each other as possible.

Why is that? Don't they like each other?

No, it's because they are trying to spread out into the whole room.

And later:

…and you said that liquids contain particles? Did you say they move, what did you say about the particles in liquids?

Er, they're quite, they're further apart, than the ones in erm solids, so they erm, they try and take the shape, they move away, but the volume of the water doesn't change. It just moves.

What about the particles in the gas?

The gas, they're really, they're far apart and they try and expand.

Bill had only learnt about particles recently in science, but seemed to have already developed a habitual way of talking about them with anthropomorphism: as if they were conscious agents that strived to fill rooms, escape bottles, and take up the shape of containers.

To some extent this is surely a lack of familiarity with objects that can have inherent motion without having an external cause (like a projectile) or internal purposes (like animals) and/or having a suitable language for talking about the world of molecular level particles ('quanticles'). Such habits may be harmless, but it is a concern if such habitual ways of talking and thinking later come to stand for more scientific descriptions and explanations of natural processes (what has been called strong anthropomorphism).

Bill's lack of a suitable language for talking about particle actions could act as a learning impediment (a deficiency learning impediment), impeding desired learning.

A dusty analogy – a visual demonstration of ionisation in a mass spectrometer

Keith S. Taber

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.

A compound is just a lot of different elements put together

Keith S. Taber

Bert was a participant in the Understanding Science project. When interviewed in Y10 he reported that he had been studying electrolysis in chemistry:

"that's where different elements are, are taken out from a compound…there's a positive anode and a negative cathode. And what it does it attracts the positive part of the compound to the negative cathode, and the negative part goes to the positive , to, you know, so that they can erm get the different elements in the different places, so they can just have one element on its own".

To fully understand what this means from a chemical context the learner needs to appreciate the chemical distinction between elements, compounds and mixtures, so I asked Bert what he thought a compound was:

It's erm, it's er two, er you know, it's just a lot of different elements put together – to create just one.

So if I went and got some elements, let's say I went and got a little file of carbon, a little file of sulphur, a little file of copper, er a little file of magnesium and I were to mix them into a beaker, maybe get a glass rod, give it a good stir, er, give me a compound?

Erm, so it's carbon, erm, carbon, sulphur, magne¬. Carbon, er – What's the fourth one?

Carbon, sulphur, magnesium and copper I think I said.

And copper. All right, erm. Copper, copper sulphate and – and carbon, and I think carbon and magnesium might go just as elements.

Okay, so if I ignored the carbon and magnesium,

Yeah.

if I took some copper and some sulphur,

Yeah.

and mixed them up together,

Yeah.

then I'd get copper sulphate.

Yeah.

And that's a compound now?

Yeah.

In chemistry there is a crucial difference between a mixture and a compound: one which it appeared Bert had not at this point acquired. Presumably his chemistry teacher, in teaching the topic of electrolysis was assuming students in the class would apply prior learning about the difference between elements and compounds, so as to appreciate the significance of electrolysis as a technique which brings about an energetically unfavourable chemical change. This prerequisite knowledge appeared to be lacking for Bert, which provided a deficiency learning impediment when it came to understanding the teaching on electrolysis.

Read about learners' alternative conceptions