GoalExplain that heating can melt a solid into a liquid and that cooling can freeze it back, and test which of two places melts ice faster.
New words
melt · to change from a solid into a liquid when it gets warmfreeze · to change from a liquid into a solid when it gets very coldheat · warmth that makes things hotter
Explanation
Some solids change when they get warm. Ice, butter and chocolate all melt. When a solid melts, it turns into a liquid. A cold cube of ice melts into water in a warm place. A liquid can change back into a solid if it gets cold enough. We say it freezes. Water freezes into ice in a freezer. Melted chocolate gets hard again when it cools down. Melting and freezing are changes that go both ways. Hot things can burn you, so a grown-up must always do the heating.
Worked examples
An adult warms a piece of butter in a pan. The solid butter melts into a yellow liquid. When it cools down, the butter turns solid again.
Sara forgets her ice cream in the sun. It melts and drips. An ice cream in the freezer stays solid because it is very cold.
On a cold night a puddle can freeze into ice. In the morning sun the ice melts back into water.
Class activity
Which place melts ice faster? (with an adult): take two ice cubes of the same size and put each in its own small bowl of the same kind. Put one bowl in a warm place, such as a sunny window, and one in a cool place, such as a shady corner. First say your prediction. Look after 10, 20 and 30 minutes and write what you see. You change only the place. You keep the bowls and the ice cubes the same. Was your prediction right?
Practice
1
What do we call it when a solid turns into a liquid?
Melting.
2
What happens to this when it gets warm?
It melts and becomes a liquid.
3
Tom puts a bowl of water into the freezer. What will it become?
Ice. The water freezes into a solid.
4
In the investigation, two ice cubes are put in a warm place and a cool place. Name one thing that must stay the same to make it fair.
For example: the size of the ice cubes, or the type of bowl, or the time you look.
