9“Let it Snow” Rules 1. No throwing snow 2. No walking in the snow 3. No eating snow……….yuck!!!!!!!!4. Act like MATURE 7th graders.
10Water Cycle Review 1. Condensation 2. Evaporation 3. Transpiration Water vapor cools and changes back into liquid droplets (how clouds form)2. EvaporationLiquid water changes into water vapor3. TranspirationPlants release water vapor into the air4. PrecipitationRain, snow, sleet, or hail falls from the clouds to Earth’s surface
11Humidity 1. Humidity (pg. 37) in book 2. As water evaporates Amount of water vapor or moisture in the air2. As water evaporatesHumidity of the air increases3. Warmer air holds more water vapor4. Colder air holds less water vapor
12Relative Humidity 1. Relative Humidity Amount of moisture the air holds compared to the maximum amount it can hold at that temperatureAmount of water in the air ÷Amount of water the air can hold x 1002. SaturatedWhen air holds all the water that it can hold at that temperatureSaturated air has a relative humidity of 100%
13Water Vapor Versus Temperature 1. If the temperature stays the same-Relative humidity changes as water vapor enters and leaves the air2. The more water vapor that is in the airThe higher the relative humidity is3. Relative humidity is affected by changes in the temperatureIf water vapor in the air stays the same,Relative humidity ↓ as temperature ↑Relative humidity ↑ as temperature ↓
14Bell Work What is relative humidity? Does warm air hold (more or less) water vapor than cold air?
15Measuring Relative Humidity 1. Psychrometer2. Instrument used to measure relative humidity
16Measuring Relative Humidity 1. Sling Psychrometer2. Has 2 thermometersA. Dry bulb measures temperature
17Measuring Relative Humidity E. If there is more humidity in the air, the water in the cloth will evaporate less and there will be little temperature changeSling PsychrometerB. Wet bulb is covered with a damp clothC. As air passes over the wet-bulb, the water in the cloth begins to evaporate, and the thermometer begins to coolD. If there is less humidity in the air, the water in the cloth will evaporate more quickly and the temperature will drop
18Measuring Relative Humidity Amount of water in the air ÷Amount of water the air can hold x 100
19Measuring Relative Humidity 1. Psychrometer-a. Find the dry bulbreading-b. Find the wet bulb-c. Find the difference-d. Find RH
21Bell Work Fill in the blanks If the humidity is low, a ______amount of water will evaporate from a wet-bulb thermometer and the _____ between the wet-bulb reading and the dry-bulb reading of the psychrometer will be high.If the dry bulb reads 10 C, and the difference between the thermometers is 8 C, the relative humidity is_______.
22Condensation 1. Process when a gas, like water vapor, becomes a liquid 2. Before condensation can occur, the air must be saturated: it must have a relative humidity of ___100%_____3. Condensation occurs when saturated air cools
23Dew Point1. Air can become saturated when water vapor is added to the air……or when it cools to its dew point2. Dew Point-temperature to which air must cool to become saturatedExample……
24Dew Point 3. Before it can condense, water vapor must have a surface to condense on
25Bell Work What is condensation? What is dew point? Can you find dew in the air?
26Making DewThe ice brought the temperature of the can down to dew point and the moisture in the air condensed.It formed from the water vapor in the air.The other items in the room were not at dew pointIt is the temperature at which dew forms.Lower
27Making Dew 6. All the items would be wet. 7. When you take a hot shower or bath, you add moisture to the air and it condense on the cold mirror.8.At night, these things cool down to the dew point temperature and the water vapor in the condenses on them.9. No, not all things can cool down to dew point.
28Making Dew10. Dew does not fall, it forms11. It evaporates
29Making Frost 1. It formed from water vapor in the air 2. Yes 3. The temperature of the can was below freezing point4. Both are formed from water vapor in the air. They both form on cool surfaces.5.Dew is a liquid. Frost is a solid.
30Making Frost6. No. Frozen dew would look like frozen drops of water. Frost is made of tiny crystals. When dew forms and then freezes, frozen dew is created. Frost is formed when water vapor turns directly into a solid, skipping the liquid phase. (sublimation)7. Dew is formed when water vapor in the air condenses of surfaces that have cooled down to dew point. Frost is formed at freezing point
31Making Frost8. Frost forms on objects at Earth’s surface. Snow forms in the atmosphere and falls to the ground.9. Snow
32CloudsClouds-Are a collection of millions of tiny water droplets or ice crystals