Year 4 know that water freezes at 0°C and boils at 100°C. Today's question is whether every material can change state. The teacher plays three short clips on the board, chosen in advance on YouTube and shown full screen: iron, which melts at 1,538°C, pouring glowing from a foundry ladle into a mould; a spoon made of gallium, a metal that melts at about 30°C, sagging and running into a mug of warm water; and liquid nitrogen, which boils at minus 196°C, bubbling fiercely in a bowl at room temperature. The teacher pauses each clip and replays the moment of change at quarter speed, using YouTube's playback setting, the iron running like water into the mould, the moment the spoon's bowl sags and the nitrogen boiling away in a room that feels cool to us, and explains that the white mist over the bowl is tiny drops of water from the air, because nitrogen gas cannot be seen. Children mark iron, gallium and nitrogen on a temperature line in their books, not drawn to scale, that already shows 0°C and 100°C, write each one's state at a room temperature of 20°C, and finish with a sentence on what it would take to turn each into a liquid.
This page is one of a growing set of PICRAT examples by cell, subject and grade. Page maintained by Andy Perryer.