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Discovering how removing heat can turn a liquid back into a solid.
Imagine you have a cup of juice. If you leave it in a very cold place, it doesn't stay a drink—it turns into a hard, crunchy snack! How does a liquid 'freeze' into a solid?
Everything around us is made of tiny bits of matter. In a liquid, like water, these bits move around easily and slide past each other. To turn a liquid into a solid, we have to take away its heat. This is called cooling. When water gets cold enough, the tiny bits slow down and stick together. This process is called freezing. When water freezes, it becomes ice. We aren't adding 'cold'; we are just taking away the heat!
Quick Check
To make a liquid turn into a solid, do we add heat or remove heat?
Answer
We remove heat (cool it down).
Liquids and solids look and feel very different. A liquid is 'runny.' It takes the shape of whatever container it is in. If you pour water into a round bowl, the water becomes round! But a solid has its own fixed shape. Ice is hard and stays the same shape unless it melts. While you can pour liquid water, you cannot pour a block of ice!
1. Fill a plastic tray with liquid water. Notice how the water flows to fill the squares. 2. Put the tray in the freezer where the air is very cold. 3. Wait for the freezer to pull the heat out of the water. 4. After a few hours, the liquid is gone and you have solid ice cubes!
Quick Check
Which one keeps its own shape: liquid water or solid ice?
Answer
Solid ice keeps its own shape.
Scientists use thermometers to measure how much heat is in something. Water doesn't just freeze whenever it feels like it; it has to reach a special temperature called the freezing point. For water, this happens at (). If the water stays warmer than , it stays liquid. If it gets colder than , it turns into solid ice!
Imagine a rainy day followed by a very cold night: 1. Rain creates a liquid puddle on the sidewalk. 2. At night, the air temperature drops to . 3. Since is less than (), the puddle loses its heat to the cold air. 4. By morning, the liquid puddle has frozen into a solid, slippery sheet of ice.
What happens to the tiny bits of water when they freeze?
At what temperature does water turn into ice?
A solid takes the shape of any container you put it in.
Review Tomorrow
In 24 hours, try to explain to someone why a puddle turns into ice on a cold night. Remember to mention 'heat'!
Practice Activity
With an adult, put a small toy in a cup of water and place it in the freezer. Check it every hour to see how the liquid changes into a solid!