Day 29 The weatherman says today’s relative humidity is 70 percent. What does that mean? The air is 70 percent saturated. Can warm air hold more, less, or the same amount of water vapor as cold air? Warm air can hold more water vapor than cold air. What does “saturated” mean? Air is saturated when it holds as much water vapor as it can. What is humidity? the amount of water vapor in the air 1

Condensation & Dew Point Investigation 6, Part 3a Water in the Air

Review Condensation How do you know there is water vapor in the air? Because liquid water appears when water vapor in the air condenses. How can you get water vapor to condense? Create a cold surface. Is heat transfer involved in condensation? Yes, heat transfers from water vapor molecules to the cold surface. Daily Warm-Up Exercises 3

Evaporation & Heat Transfer During evaporation, heat transfers from the environment to the water molecules. For example, when water evaporates from your skin, the water molecules gain energy, move faster, and change from liquid to gas. Molecules in your skin lose energy and slow down, which makes your skin feel cooler. Daily Warm-Up Exercises 4

Condensation & Heat Transfer During condensation, heat transfers from the water molecules to the environment. For example, when water vapor condenses on a glass, the vapor molecules lose energy, slow down, and change from gas to liquid. Molecules in the glass gain energy and move faster, which makes the glass warmer. Daily Warm-Up Exercises 5

Condensation Temperature Discuss these questions with your partner: Is there a temperature at which condensation starts to happen? Will condensation take place at any temperature if you allow enough time for heat transfer to occur? Daily Warm-Up Exercises 6

Procedure Record the temperature of a half cup of water. Add 1 ice cube and stir carefully with the thermometer while watching the temperature. If the ice melts, add another ice cube. Continue adding 1 cube at a time until you see condensation on the side of the cup. Daily Warm-Up Exercises 7

Procedure The moment you see condensation, remove the ice cube and record the temperature. Pour the water into an empty, dry cup. If condensation forms, record the water temperature and pour the water into another empty, dry cup. Continue until no condensation appears. Daily Warm-Up Exercises 8

Sample Data Table Condensation Temperature (yes or no) Daily Warm-Up Exercises 9

Dew Point Calculate the average of everyone's highest condensation temperatures. This temperature is the dew point. What is dew? water that appears on plants and other surfaces in the morning How does dew form? water vapor condenses on cool surfaces Dew point is the temperature at which water vapor condenses. Daily Warm-Up Exercises 10

Dew Point Dew point can also be described as the temperature at which air is saturated with water. When air cools to the dew point temperature, water vapor in the air will condense. Dew point depends on the amount of water vapor in the air. Humid air will condense at a higher temperature than dry air. Daily Warm-Up Exercises 11

Dew Point Questions Turn to Dew Point Questions (page 35 in your lab notebook). Answer the questions. Daily Warm-Up Exercises 12