1. Relative Humidity

2. Hot Air Warm air has more energy and more space between each molecule. Warm air has more energy and more space between each molecule. It can hold more water vapor than colder air It can hold more water vapor than colder air More Water

3. Cold Air ► Cold air has less energy and the molecules are closer together. ► It can’t contain as much water vapor as warmer air can. Less Water

4. It Depends Relative humidity is how much water vapor is in the air compared to how much there could be if the air was saturated or “full.” Relative humidity is how much water vapor is in the air compared to how much there could be if the air was saturated or “full.”

5. Hot vs Cold ► A relative humidity of 50% on a hot day would mean there was more water vapor in the air than 50% relative humidity on a cold day. It would be wetter

6. Dropping Temperature ► So, if the amount of water vapor stays the same but the temperature goes down, the relative humidity would go up

7. Rising Temperature ► If the amount of water vapor stays the same and the temperature goes up, the relative humidity will go down.

8. The most water in the air Even on the hottest day, with very high relative humidity, the percent of the air that is water vapor is never more than about 4%. Even on the hottest day, with very high relative humidity, the percent of the air that is water vapor is never more than about 4%. 4%

9. Measuring Humidity You can measure the relative humidity by figuring out how much water can evaporate into the air around you at a given temperature. You can measure the relative humidity by figuring out how much water can evaporate into the air around you at a given temperature. The difference in temperature between a dry thermometer and a wet thermometer can be used to calculate the humidity. The difference in temperature between a dry thermometer and a wet thermometer can be used to calculate the humidity.

10. If the air already has a lot of water vapor in it, not much new water can evaporate. If the air already has a lot of water vapor in it, not much new water can evaporate. If the air is “dry” lots of water can evaporate. If the air is “dry” lots of water can evaporate. It takes heat from the air to help water It takes heat from the air to help water evaporate making the temperature of the temperature of the thermometer go down.