A research base for new objectives of science teaching

Abstract

A bright year 7 student was going through the usual steps that lead to the concept of density and its values for wood and brass and aluminium. After mensurating the volumes of cuboids of these materials he was observing the volume of liquid they displaced in a measuring cylinder. As he carefully pushed the wooden cuboid below the surface, I asked him, “Why do you have to push the wood down?” “Because it floats otherwise”, he replied. “Why didn't you have to push the aluminium down?” “Because there was not enough water to make it float”. “Tell me more”, I said. “Well, sir, you must have seen metal ships floating on the sea. If there's enough water, metal will float, but not in a little bit like this”.

Just after describing for me how liquid acetone evaporated if it is placed on your skin, a first year university chemistry student with good test results was unable to give me any examples of a liquified gas. When pressed he muttered “Solids, liquids, gases” (A strangely immutable sequence that has neither evolutionary nor biblical support.) and said he thought the cO in a cylinder was probably liquid. Gases could be liquified by lowering the temperature, he said. On being asked to describe what would happen if he steadily cooled down the air in a space, he began by quoting, “Air molecules, being particles moving very rapidly with energy proportional to temperature”. As he cooled them down in thought, he held out his hands and slowed down the vibration of his fingers about a point in space. Finally, his fingers stopped and he said, “It's nothing”. “What do you mean, has it disappeared?” I said. “No”, he replied, but it's no longer a gas, and it's not a liquid or a solid. They are all just there suspended in space. It's no-thing”.