Lesson 55: Condensation and the Water Cycle
Condensation returns water vapor to liquid, while frost can form directly as ice. Dew, cold surfaces, and evaporation connect these processes with the movement of water through Earth's water cycle.
Key Ideas
- Condensation changes water vapor into liquid water. Drops on a cold glass can form from vapor in the surrounding air.
- Water is still water when it evaporates or condenses. Its state changes, but it does not become a different substance.
- Cooling moist air can lead to condensation. Frost can form when water vapor changes directly into ice on a very cold surface.
- The Sun supplies energy for evaporation, and gravity pulls water downhill. Both help keep water moving around Earth.
- Evaporation leaves most dissolved salt behind. Water with little salt can still contain harmful substances or germs.
Vocabulary
- Condensation: The change from water vapor to liquid water.
- Dew: Drops of water that form when water vapor condenses on a cool surface.
- Frost: Ice crystals that can form directly from water vapor on a freezing-cold surface.
- Water cycle: The repeated movement of water between air, land, oceans, ice, and living things.
- Precipitation: Water falling from clouds as rain, snow, sleet, or hail.
- Fresh water: Water with very little dissolved salt. Fresh does not automatically mean safe to drink.
Discussion Questions
- Car windows fog up on the inside when several people are in the car on a cold day. Which side of the glass does the water come from, and where did the vapor come from?
- Design a small solar still that collects condensed water from salt water. What would it model, and what contamination could remain?
- Water cycles among Earth's stores, while energy flows through the system. Why does continuing water movement need an energy supply?
Supplies
- A glass, ice, water, a good pinch of salt, a paper towel, and a cold window or mirror
- A dishpan, hot water, a glass of ice water, and an adult to handle the hot water