Our world is a watery one! Water makes up all our lakes and oceans and our ice and snow. There is also a lot of water floating in the air. We can’t see it because it is in a gas form called water vapor.
Sometimes, in the early morning, you might notice tiny water drops clinging to blades of grass, to flowers, to decks, and to railings. Where did they come from? It may have rained the night before, but often they can happen without any rain at all!
At nighttime, the temperature drops because the Sun isn’t shining. The surfaces of grass blades and flower petals cool down, and that can cool the water vapor in the air around them. When the water vapor in the air cools it does something called condensing. The tiny particles of water in the air come together and they form a liquid drop. When water condenses high in the sky, it forms clouds and rain. When it condenses on cold surfaces, it becomes drops of dew.
We usually see them in the morning because by the time the afternoon rolls around, the Sun heats the dew and it evaporates, or turns back into water vapor floating in the air.
If dew forms when the temperature is below freezing, it forms as frost. Frost is just like dew, but instead of tiny water drops on the grass, you see tiny crystals of ice!
ExplorationWater’s Weird Ways
What different forms of water do you run into every day? Water is probably liquid in your bathtub and ice when you use it to cool your drinks.
If you have a hot day, try taking a glass of ice water outside (make sure you check with a grown-up to see if it’s okay.) The difference in temperature between the ice water and the air should cause something interesting to happen to water vapor in the air that touches the outside of the glass. What do you think will happen? Think about condensation.
If a hot day is months away, and you find yourself with very cold weather, think about what happens when you exhale (breathe out) on a very cold day and you see your breath. What do you think you’re actually seeing in the air?
Sources & links
"dew." Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. 14 Nov. 2009 "dew." Merriam-Webster Online Dictionary. 2009. Merriam-Webster Online. 14 Nov. 2009. Horstmeyer, Steven L. “About Frost.” SHorstmeyer.com. 14 Nov. 2009.