This is a transcript of a conversation that took place between myself and three Year 5 pupils in Sheffield in 2019. The pupils were experienced in Philosophy for Children – they had practiced dialogue before. They had learned about changes of state in their science lessons. I asked them to sort some scenarios according to the changes of state involved. The transcript focuses on the conversation around just one of the cards.
One pupil, P3, is reserved and contributes infrequently. The others, P1 and P2, have different perspectives on what freezing means. As their teacher, T, I am facilitating their conversation and hoping to deepen their understanding of the concept of freezing.
P1: So this one… lava turns into new rock after a volcano has erupted
P2: Probably freezing ‘cos it cools down – to turn into the rock
P1: It wouldn’t quite freeze, but it would cool down – so I reckon it’s kind of freezing. It’s sort of freezing.
T: Why aren’t you sure – why do you say kind of freezing?
P1: Because it isn’t turning to ice, it’s cooling down just a little bit, just enough to turn it back into rock, rather than it actually freezing
T: Do either of you disagree with that?
P2: I think it might be freezing
P1: So it’s half on, half off then, because it’s cooling down, but not freezing.
(Coming back to the problem a few minutes later, after discussing others)
P1: So it’s still not freezing, but it’s a hard one…
P3: Could it evaporate all the liquid that was in the lava?
P1: I don’t know whether the liquid would evaporate, but it might, ‘cos, actually… I’m not sure
T: Tell me again – earlier you said you thought it was freezing but not really freezing…
P1: It’s just cooling down
T: What is freezing?
P1: Freezing is when the temperature goes below zero in water, or a liquid solidifies
T: Does anybody disagree with that? Does anybody have a different view?
P2: Well, just to go against you a bit, you said liquid solidifies and lava is technically liquid and it has solidified
P1: Yes, so that’s solidifying, but that doesn’t necessarily mean it’s freezing
T: You’re making a distinction there between something solidifying as it cools down and something freezing.. Why is that not freezing?
P1: That just returns to the state it was in before, which was rock, because it’s been melted – the rock seems to have been melted and churned up by the lava from the volcano, and then it’ll get cooler, but not freeze, and it’ll just return to the state it was in before.
P2: I think it probably would be freezing, ‘cos freezing, it doesn’t have to be minus temperatures – if it’s just cooling it is sort of freezing
P1: I still disagree with that because the science behind freezing is that things get so cold that they solidify, and this isn’t what’s happening – it just returns to its normal state, because it’s been heated up, but it cools down slightly or…
T: You just said freezing means that things get so cold they solidify, but this isn’t that because it’s just returning to its normal state because it’s cooled down quite a lot. What’s the difference?
P1: It’s not… It hasn’t… The temperature hasn’t gone below freezing, it’s just… it hasn’t actually frozen.
T: Right so this is the issue, one of you is suggesting that freezing is something that happens at zero degrees C or below, and you seem to be suggesting ‘well not necessarily’. Can you give any examples of anything freezing other than water that might happen at a different temperature?
P2: Well, like chocolate, when you take it off the heat and just leave it, if you leave it for a matter of time it could even be twenty degrees, it would just set
P3: It would just solidify to its normal state
P2: Yeah
T: A bit like the lava – but would it have to be at zero degrees to do that?
P2 & P3: No
T: But it’s still freezing?
P1: It’s not freezing
T: What about if I took gold, and I don’t know what the melting point of gold is, but it’s about 900 degrees C, and I heat the gold up and at nine hundred degrees C or thereabouts it turns into liquid gold, and then I leave it to cool down again and it turns back to solid gold. Is that melting and freezing or is that something different?
P1: It’s just melting and cooling down.
T: Why is it melting then? You’re happy with the word melting for something changing from a solid to a liquid at a temperature that’s not zero
P1: Because it’s melting, because the temperature’s hotter than it should be.. I’m… I’m confused now.
At this point I return to an authoritative explanation of freezing, with reference to the examples that have been shared.
