1. Evaporation: Water on Earth's surface evaporates, transforming from liquid to gaseous water vapor.
2. Condensation: As the water vapor rises in the atmosphere, it cools. The cooler air can't hold as much water vapor, so the vapor condenses back into tiny liquid water droplets. These droplets form clouds.
3. Freezing: Within the clouds, temperatures drop below freezing (0°C or 32°F). The liquid water droplets in the cloud freeze into tiny ice crystals.
4. Growth and Aggregation: As these ice crystals fall through the cloud, they collide with other water droplets and ice crystals. They absorb more water vapor, which freezes onto their surface, causing them to grow larger. Multiple ice crystals can also stick together (aggregate), forming snowflakes.
5. Precipitation: When the ice crystals and snowflakes become large and heavy enough, they fall from the cloud as snow.
Why it's a Physical Change:
* No new substances are formed: Snow is still water (H₂O), just in a different state (solid). The chemical composition of water doesn't change during the process.
* The change is reversible: If you melt snow, it turns back into liquid water. This demonstrates that the change in state is temporary and doesn't involve the creation of a new substance.
Key Points:
* Temperature is crucial: The freezing point of water is key to snow formation.
* Air currents and cloud type: The movement of air within the cloud affects how the ice crystals grow and how they fall as snow.
Let me know if you'd like me to elaborate on any of these steps!
