"The resources budget has been cut," said the head.
"Tell me the bad news."
"There's 50p left for science."
"50p! What about the time machine I was buying for Year 3?"
"Sorry. That will have to go. But I've arranged a discount with the corner shop. You know, the family with that lovely lad in Year 4."
"What can I buy for 50p? A can of cola?"
"Well, you could do worse..."
Sugar and vegetable extracts are among the main ingredients of cola. Every can lists its ingredients and nutritional content. Carbonated water and caramel colouring come first, then the sweeteners and flavourings - including citric acid - and a dash of preservative. Last on the list is a small amount of caffeine. Questions about what the drink contains (a fair amount of energy food), and what it doesn't contain (any protein or fat I no carbohydrate in a diet cola), are a novel way of tackling a food topic.
But does cola rot your teeth? There has always been concern about fruit drinks and teeth. Teeth suspended in fruit drinks of all kinds are supposed to rot away at amazing speed. Since cola is an acid drink, it is not surprising if it does the same. It would happen with vinegar or fresh orange juice, but nobody suggests that we stop consuming them. The chances of holding cola in your mouth overnight while it eats away your dentine seem pretty slim; the main damage would be from the sugars it contains. And this is true of many foods. Sugar sticking to your teeth, even fruit sugars, can be rapidly converted to acids by bacteria. So the problem would seem to come from a lack of mouth hygiene - not the sugar itself.
Drinks cans are made from aluminium, which is extracted from the mineral bauxite after expensive electrical process, so recycling cans is environmentally friendly. While aluminium producers can be exemplary in their repair of the landscape after open-cast mining, they still have to excavate substantial areas, some of them in sensitive rainforest regions. It takes more than 2kg of bauxite and a huge amount of electricity to yield half a kilo of aluminium.
Look around and see where else aluminium is used - bottle caps and milk-bottle tops; ladders, window frames, guttering and other building uses of all kinds; aeroplanes, boats and cars.
This remarkable material is a light metal that conducts electricity well (only copper and aluminium are good enough conductors for electrical circuits) but is not magnetic. It conducts heat well and is ideal for making cooking utensils.
Aluminium has many properties which make it suitable for this use, including:
* It is light, making the cans easy to carry and cutting transportation costs.
* It is strong, so the cans can be stacked and handled easily.
* It can be rolled into sheets and moulded into shape, and holes can easily be cut in it for ring-pulls.
* It resists corrosion - it is not affected by the drink inside the can, nor by packing the can with ice or putting it in the fridge.
* It is non-toxic. It doesn't harm our bodies, and is even used in medicines such as indigestion tablets.
* Paints and transfers of all kinds will "take" on aluminium, so the drinks manufacturer can record brand information on it. It can be embossed with raised letters or moulded into shapes.
* It can be recycled for use again and again.
Aluminium is a conductor of electricity, but it is not magnetic and it doesn't corrode. If it is scratched or damaged, it forms a thin coat of oxide on its surface that prevents further decay. You can test it for electrical conductivity and magnetism in the classroom. Aluminium reflects 80 per cent of the light that falls on it, so maybe science from a 50p cola can isn't so dull after all.
There are other physical processes you can investigate. For example, the can is shaped for strength. It will take an enormous force, end-to-end, before it can be crushed. Put a strong wooden board on four cans and try standing on them.
Many colas contain caffeine, which is also found in coffee. This drug has marked effects on the body, one of which is to increase in heart rate. Ask some children to drink a cola (with parental permission); and, for control purposes, ask others to drink the equivalent amount of water. Take their resting heart rates before drinking, and again half an hour after each drink. If they have not been active while the caffeine had its effect, then there should be a measurable difference between the heart rate of the cola drinkers and the water drinkers. Is this also true of caffeine-free cola?
With thanks to Linda Atherton and the Warwickshire primary teachers who found 100 uses for a can of cola
Cans of ordinary cola sink but cans of diet cola float. Why? When faced with this challenge, children can investigate a range of hypotheses:
*There is more cola in a can of ordinary cola - so let's pour it into a volume measure and compare it with the contents of a can of diet cola.
*There is more gas in diet cola - so let's open each can inside a plastic bag and see how much the bags inflate.
*The cans might be made from different materials - so let's try a magnet on both types.
*There's a difference between sugar crystals and sweetener crystals - so let's look at crystals from sugar and sweeteners under a binocular microscope. Sweetener crystals are often delicate and needle-shaped
*Sugar makes real cola heavier - so let's investigate the weight of equal volumes of cola and diet cola (their comparative density).
It indeed appears to be the sugar in cola that makes it sink.
Aluminium is one of the commonest - yet one of the hardest to get at - metals on Earth.
In the US, it is pronounced "ah-LOO-min-um". This was the original name Sir Humphry Davy gave to the metal when he discovered it. Only later did he change it to aluminium.
An aluminium can is one-third of the weight of a steel can.
Recycling a single can saves the energy needed to burn a 100-watt light bulb for three and a half hours.
A full cola can combines solid, liquid and gas.