Water in the Air Water in the Air…
Water in the air experiment discussion - Where did the water on the outside of the cups come from? How do you know?
During the experiment you found that the water on the outside of the glass and the puddle on the table did not come from inside the glass. The water level inside the cup didn’t change as the puddle formed. It wasn’t the same color! The water on the glass and in the puddle came from the air around the glass. How did that happen? When the warm air touched the cold glass, the air cooled. When the air cooled, droplets of water formed and ran down the side of the glass and made a puddle on the table. Water in the air...
Focus Question - How does water get into the air?
Copy the question in your notes and make a claim based on what you already know.
Example...I think that water gets into the air by… How does the water get into the air?
What do we call the water in the air? It is called water vapor. Water vapor is really just water in the form of a gas. It is invisible, colorless, odorless, and tasteless. The amount of water vapor in the air is called humidity.
So, how does this water get into the air in the first place? Think about the planet Earth. More than ⅔ of the Earth is covered with liquid water. Most of this water is found in the oceans, but the rest can be found in lakes, rivers, or even in the ground. The rest of the land is covered with plants. Plants also contain water. To get into the air, this liquid water must be changed into a gas (water vapor). How does the water get into the air?
The changing of a liquid into a gas is called evaporation. This takes lots of energy. This energy comes mainly from the Sun. Each day, the Sun turns trillions of tons of ocean water into water vapor. The Sun’s energy give the molecules of water a “lift” into the atmosphere as water vapor. When the water vapor molecules cool down, they change back into liquid water and return to the surface of the Earth. This is called condensation. Condensation is the changing of a gas into a liquid. Can you see condensation happening? Sure! Have you ever seen frozen food held over hot water? What do you notice? You probably saw a cloud form! This is condensation!
Video - Condensation So what about the plants?
The plants also contain water. Plants’ roots absorb water that has seeped into the ground. Plants transport the liquid water through their roots and stems into their leaves. The leaves then give off water in a process called transpiration. Transpiration is the second largest source of water vapor in the atmosphere. What is the largest source??? The oceans!
Video - Transpiration How much water can the air hold?
Does water just keep evaporating from a puddle, lake or ocean? YES! Does this mean that the amount of water vapor in the air keeps increasing without a limit? NO!
One reason is condensation. As Earth’s water evaporates, water vapor in the atmosphere is condensing at the same time. The warmer the water is, the greater the evaporation. So, warmer air can hold more water vapor than colder air. Why can air feel sticky?
The higher the relative humidity, the less water that can evaporate into the air. So sweat can’t evaporate from our skin as easily. This make the air feel wetter or sticky.
Have you ever heard people complain on a hot day, “It’s not the heat, it’s the humidity!” When the sweat evaporates from our skin, it takes the heat away from our skin, so we feel cool. When water vapor condenses on our skin, it adds heat to our skin so we feel hotter. On days where the humidity is high, sweat doesn’t easily evaporate from our skin so we don’t feel cool….unless we are in a breeze!
Brainpop - Humidity Water in the Air - Vocabulary
★ Water vapor – water in the form of a gas ★ Humidity – the amount of water vapor in the air ★ Evaporation – the changing of a liquid into a gas ★ Condensation – the changing of a gas into a liquid ★ Transpiration – evaporation of water from plants Water in the Air - Notes
➔ When cool and warm air meet, the lighter warm air is pushed higher in the atmosphere. ➔ Whenever warm air rises and cools, the water vapor in the air condenses. ➔ Water droplets in the air form clouds. ➔ Transpiration is the process that plants use to add water vapor to the atmosphere Water in the Air
Discovery Education - Video
Weather Things: Sun, Air, Wind and Atmosphere - (27:36)