When Years 5 and 6 at Quinton Primary School in south Warwickshire were studying "Gases around us" for science, their teacher presented them with a challenge.
If air really existed, then surely it should be possible to empty it from a plastic cup? The children came up with various ideas in response to the question.
"You could spoon it out." Nice idea, but the more they spooned, the more they suspected that the cup was simply filling up again.
"You could pour it out." Good thinking, but they couldn't be sure that the air had all gone; indeed, they suspected that it was rapidly refilling as they poured it out. You can pour air, although you will have to do it underwater and upside down. Then a bubble will "pour" up from the cup.
"You can suck it out." This was a neat idea, but after a lot of hard sucking - and some red faces - the cup was still full of air. Maybe if they had sealed the top of their cup around a straw they could have sucked a vacuum - a pump is certainly able to do this.
"You can push it out." Several groups came up with successful ideas for displacing the air with water or play-putty - fill the cup, and all the air has gone.
This challenge met, the children then looked at using displacement to find just how much air there was between collections of objects in their cups.
Using loosely packed plastic play bricks, marbles and pebbles, they filled each cup and then poured in water to the brim to push out the remaining air. Then they measured the water from each cup to see how much air they had displaced by using the bricks, pebbles and marbles.
They tried each set of objects more than once, finding surprising differences. "We think it depends on how well they are packed," said the children. If you put in the plastic play bricks carefully, they took up more space than if you poured in a handful, and so there was less room for air and water. But closely packed marbles left fewer spaces than loosely packed play bricks.
In the process, pupils confirmed that air does exist; that it takes up space; and that it can be displaced using a liquid or a solid. They also found it was worth doing investigations more than once (an important principle of scientific enquiry) because there can be surprising differences between results, and that the results can be recorded in a number of forms, including graphs.
With thanks to Jenny Hudson and class 4 at Quinton Primary School.