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 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”.
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”.
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”.
Just over a year later (in Y8) Sophia had been studying “that different erm substances have different freezing and melting and boiling points, and some aren’t like a liquid at room temperatures, some are a solid and some are a gas and things like that".
I: Give me an example of something else that’s a solid at room temperature?
Sophia: Iron.
I: Do you think iron would have a melting point?
S: Yeah.
I: Yeah, and if I, what would I get if I, if I heated iron to its melting point?
S: It would become a liquid.
I: And why would it do that?
S: Because it’s got so hot that particles – they have spread out or something?
I: So what do you think would happen if I heated the iron liquid?
S: It would stay a liquid.
I: No matter how much I heated it?
S: It might, I don’t know if it would become a vapour.
I: Can you get iron vapour?
S: No, I don’t think so.
I: You don’t think so?
S: No.
So it seems that Sophia had shifted from accepting that iron would partially evaporate (when learning about the particle model of the different states), to considering that iron can not become a vapour. The notion of iron as a gas is not something we can readily imagine, and apparently did not seem very feasible. In part this might be because we think of iron the material (a metal, which cannot exist in in the vapour phase) rather than as a substance that can take different material forms.
It seems Sophia's prior knowledge of iron the material was working against her learning about iron the substance, an examples of a grounded learning impediment where prior knowledge impedes new learning.
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Dr Keith S Taber kst24@cam.ac.uk
University of Cambridge Faculty of Education