Break the ice
How do we get science pupils thinking? At key stage 3, according to developmental theorist Jean Piaget, most pupils will be at the concrete stage of thinking: when asked to explain their understanding of whether an object floats or sinks they will tend to rely on one or two variables in their explanation: heavy objects will probably sink and light ones will float. Or they may consider size: small objects will float and large ones will sink. Asking them to consider weightmass and volumesize simultaneously will often cause confusion. How do you move them on?
As part of in-service sessions in cognitive acceleration training in the Department of Education at Keele University, I use a number of brainwarmer exercises. The Titanic activity, developed with Debbie McGregor, is particularly popular. In CASE (cognitive acceleration through science education) methodology, one stage in a lesson is "bridging", where the thinking that developed in the lesson is made explicit in an example relevant to the pupil's experience and interests. The film Titanic is part of most home DVD collections, and makes a good example for sinking and floating.
Add golden syrup to a large clear coffee-jar so that the jar is about one-quarter full. Fill one small mineral water bottle with vegetable oil and another with water coloured by a little blue food dye. Ask the class to discuss in groups (of three, mixed-gender recommended) what will happen when the water and oil are poured into the coffee jar. After a minute or so, ask two or three groups for their predictions (in CASE, this is called construction) and reasons (in CASE, metacognition). Usual responses range from one messy layer to three distinct layers with a variety of orders.
At this point, repeat and ask clarifying questions at this point - resist the temptation to comment. Then add two liquids simultaneously and, after a minute or two, three layers are apparent: syrup, water, oil. Was this as the class expected? If not, why? Have they changed their ideas after watching this (reconstruction) and why (metacognition)?
Introduce a small seedless grape as Leonardo di Grapio (Year 7 pupils enjoy the play on words) and ask them to discuss where "he" will end up if dropped into the jar. Again, get them to explain their predictions.
Introduce the term "interface" - there are four here: glasssyrup, syrupwater, wateroil and oilair. An object may also lie within a layer, so there are at least seven places where "he" may settle.
After exploring predictions and explanations with the class in a non-judgmental manner, drop "Leonardo" into the jar. A fresh grape will normally sit on the syrupwater interface. Is this the expected result? Have their ideas changed? How?
Now consider "Nut" (Kate) Winslet: what will happen if she is dropped into the jar? In discussions, pupils may ask what type of nut she is - peanut? Walnut? At this point, I show them a large metal nut to a chorus of surprise. Why are they surprised? A few will recognise that the cognitive conflict has been caused by the assumption that the nut will be food-related, like all the other objects so far.
Now discuss where the nut will settle; most decide it will go to the bottom of the jar because of its weight. Repeat this procedure with, for instance, Penny (penne) Pasta, Tom Ato, Billy Grain (rice), Paul Peanut, Sultana.
Each can cause different levels of challenge: for example, do fresh and older tomatoes behave the same? Does the orientation of the pasta matter (vertical or horizontal)? One grain of rice or a clump? Raw peanut or roasted? A sultana is a dried seedless grape - does this help in predicting?
Ask them to consider what will happen if the raisin is dropped into a glass of water. Justify any prediction from the understanding developed from the previous examples. After the raisin sinks to the bottom, ask if it would be different with fizzy water. This usually leads to a good deal of discussion. Try it: the raisin initially sinks but, as bubbles begin to nucleate on it, rises to the surface; bubbles escape and the raisin sinks again, repeating its journey.
To finish, ask them to consider the following problems at home: "how does a lava lamp work?" "Why is it easier to float in the sea than in a swimming pool?" Such questions help them reflect on how their understanding of floating and sinking has changed (metacognition) and apply it to their own experiences (bridging). I would also ask some groups to consider how this lesson differs from their usual science lessons and what they had learned about their own thinking and that of their classmates.
So engaging is the activity that you have to resist numerous proferred answers to the problems. You are looking for reflection away from the science room to reinforce the idea that science is part of everyday life and can be used to explain it. As well as addressing Sc11b and 2k to 2o, this activity moves students from a concrete level of understanding to a more abstract level. At this higher level, they must consider how the variables of weightmass and volume interact for the objects and the fluids in which they are immersed.
Barry Gunter is director of thinking programmes at Keele University