Materials can change state — Physical education, 7–10 years
Heating and cooling can change a material from solid to liquid or gas, and back again. The material is still made of the same stuff.
The same material can look different
Water is solid ice, liquid water or invisible water vapour, depending on its temperature. Heating gives its tiny parts more movement; cooling gives them less. A change of state changes how the material behaves, not what substance it is.
Why does a state change matter?
People needed to explain why puddles disappear, ice melts and steam forms without a new substance appearing. The idea of changing state links these events to heating and cooling. It helps us predict that water in a freezer may become ice, while water in a hot pan may become vapour.
From ice to water
Put one ice cube on a plate at room temperature, about 20 °C. After a while, heat from the room enters the cube, and its temperature rises to 0 °C. It melts into liquid water; weighing it would show nearly the same amount of water as before.
Melting is not disappearing
It is reasonable to think a melting ice cube vanishes because its solid shape is gone. But the water is still there, spread across the plate as a liquid. A state change can be hard to see, especially when liquid water later becomes an invisible gas.
Cooking and the water cycle
Cooking uses melting butter, boiling water and freezing food to change how materials behave. In nature, sunlight makes water evaporate from seas and puddles; higher in the sky it cools and condenses into droplets, helping form clouds. The water changes state but keeps cycling.
Keep exploring
Other languages
Loading MyLeoNes™…