Day 27 What’s the difference between water vapor and steam? Water vapor is water in the form of a gas. It is not visible. Steam is a mixture of air, water vapor, and visible liquid droplets that form when water vapor condenses. When water boils, liquid water changes to gas and joins the surrounding air. The air above the tea kettle is cool and very humid, so some of the water vapor molecules immediately condense, changing back to liquid. As the droplets move to drier air, most will evaporate, changing back to gas. 1

Evaporation & Humidity Investigation 6, Parts 1-2a Water in the Air

Design a Demonstration Discuss the following questions with your partner: Do you think there is water vapor in the air around us? How could you demonstrate that there is or is not? Daily Warm-Up Exercises 3

Teacher Demonstration Glass with colored water and a lot of ice. The outside of the glass is dry. What do you predict will happen? We'll check back at the end of class. Daily Warm-Up Exercises 4

Evaporation If there is water vapor in the air, how does it get there? Liquid water changes to gas and goes into the air. What is that process called? evaporation Daily Warm-Up Exercises 5

The Effect of Wind Get a cup of water and dampen a small area on the backs of both hands. Gently blow on the spot on your left hand to simulate the wind. What effect does wind have on the wet spot? The left spot dries faster, and the left hand feels cooler than the right. Where did the water go? into the surrounding air Daily Warm-Up Exercises 6

Evaporation Takes Heat Why did the wet spot feel cold as it dried? It takes heat to turn liquid water into water vapor. Heat transfers from your skin to the water by conduction. When your skin loses heat, you feel cold. Discuss this question with your partner: How could you use thermometers, fabric, rubber bands and water to measure temperature change during evaporation? Daily Warm-Up Exercises 7

Procedure Record the starting temperatures of the thermometers. Wrap a piece of fabric around the bulb end of both thermometers and secure with rubber bands. Dip the fabric end of one thermometer into the water. Blot excess water so it isn't dripping. Daily Warm-Up Exercises 8

Procedure Rest your elbows on the desk and wave the thermometers in the air. Wave the thermometers by moving your wrists back and forth 4 to 6 inches. Take turns, and read the temperature on both thermometers between turns. Continue for about 5 minutes. Daily Warm-Up Exercises 9

Results Calculate the difference between the starting and ending temperatures for each thermometer. What caused the temperature of the wet thermometer to go down? It takes heat to turn liquid water into water vapor. Heat transferred by conduction from the environment to the water, so the environment (thermometer, fabric, etc.) got cooler. Daily Warm-Up Exercises 10

Return to Teacher Demo What happened to the glass with colored water and ice? Unless the air in the classroom contains very little water vapor, there will be liquid water on the outside of the glass. Where did the water come from? Water vapor in the air changed from gas to liquid and collected on the side of the glass. Daily Warm-Up Exercises 11