What's it about?
Baking cakes with pupils is fun, if messy. But how many times have you encouraged parents to do some science at home using chemicals found in the kitchen cupboard? Cornflour, salt, sugar, water and red cabbage can be used to demonstrate science at home, writes James Williams.
There are many similarities between cooking and science. Changes of state (freezing and boiling) are routine observations made in a kitchen. Evaporating salt (or sugar) from water to separate the solid crystals is a simple experiment. Seeing if warm water dissolves more salt than cold water is a safe, simple investigation that can be done at home. A competition, such as who can grow the biggest salt or sugar crystal, can add interest.
A messier experiment uses cornflour mixed with water. With the right proportion of water and cornflour you find that the faster you stir, the stickier it becomes. With the right consistency, when you apply pressure to the mixture by squeezing, it appears to become more solid. When you release the pressure, it turns back to a fluid. This can be compared with tomato ketchup, which does the opposite. It is quite thick and doesn't flow well, but if you shake it hard, it flows.
Both are what scientists call "non-Newtonian fluids"; they don't behave as they are supposed to. Getting children to predict what they think will happen and to write down what they can see and, in the case of cornflour, feel is part of the process of being a scientist - making predictions, looking at what happens and noting observations.