# Weather and Climate Chapter 2 February, 2011.

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Weather and Climate Chapter 2 February, 2011

Bell Work What is condensation? What is dew point?
Can you find dew in the air?

What is weather? Weather
A condition in the atmosphere at a particular time and place

Water in the Air 1. Water in the air effects weather
2. Forms of water in the air A. Gas As water vapor B. Solid Ice (snowflakes) C. Liquid rain

Water Cycle 1. Constant movement of water from land to air and back to land again 2. Precipitation- “Let it Snow” lab

“Let it Snow Lab” Follow Directions
Equipment needed is at the lab stations Lab Safety?

“Let it Snow” Beaker

“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.

Water Cycle Review 1. Condensation 2. Evaporation 3. Transpiration
Water vapor cools and changes back into liquid droplets (how clouds form) 2. Evaporation Liquid water changes into water vapor 3. Transpiration Plants release water vapor into the air 4. Precipitation Rain, snow, sleet, or hail falls from the clouds to Earth’s surface

Humidity 1. Humidity (pg. 37) in book 2. As water evaporates
Amount of water vapor or moisture in the air 2. As water evaporates Humidity of the air increases 3. Warmer air holds more water vapor 4. Colder air holds less water vapor

Relative Humidity 1. Relative Humidity
Amount of moisture the air holds compared to the maximum amount it can hold at that temperature Amount of water in the air ÷ Amount of water the air can hold x 100 2. Saturated When air holds all the water that it can hold at that temperature Saturated air has a relative humidity of 100%

Water Vapor Versus Temperature
1. If the temperature stays the same- Relative humidity changes as water vapor enters and leaves the air 2. The more water vapor that is in the air The higher the relative humidity is 3. Relative humidity is affected by changes in the temperature If water vapor in the air stays the same, Relative humidity ↓ as temperature ↑ Relative humidity ↑ as temperature ↓

Bell Work What is relative humidity?
Does warm air hold (more or less) water vapor than cold air?

Measuring Relative Humidity
1. Psychrometer 2. Instrument used to measure relative humidity

Measuring Relative Humidity
1. Sling Psychrometer 2. Has 2 thermometers A. Dry bulb measures temperature

Measuring 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 change Sling Psychrometer B. Wet bulb is covered with a damp cloth C. As air passes over the wet-bulb, the water in the cloth begins to evaporate, and the thermometer begins to cool D. If there is less humidity in the air, the water in the cloth will evaporate more quickly and the temperature will drop

Measuring Relative Humidity
Amount of water in the air ÷ Amount of water the air can hold x 100

Measuring Relative Humidity
1. Psychrometer -a. Find the dry bulb reading -b. Find the wet bulb -c. Find the difference -d. Find RH

Bell Work 1. Which

Bell 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_______.

Condensation 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

Dew Point 1. Air can become saturated when water vapor is added to the air…… or when it cools to its dew point 2. Dew Point- temperature to which air must cool to become saturated Example……

Dew Point 3. Before it can condense,
water vapor must have a surface to condense on

Bell Work What is condensation? What is dew point?
Can you find dew in the air?

Making Dew The 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 point It is the temperature at which dew forms. Lower

Making 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.

Making Dew 10. Dew does not fall, it forms 11. It evaporates

Making Frost 1. It formed from water vapor in the air 2. Yes
3. The temperature of the can was below freezing point 4. Both are formed from water vapor in the air. They both form on cool surfaces. 5.Dew is a liquid. Frost is a solid.

Making Frost 6. 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

Making Frost 8. Frost forms on objects at Earth’s surface. Snow forms in the atmosphere and falls to the ground. 9. Snow

Clouds Clouds- Are a collection of millions of tiny water droplets or ice crystals