Right Now : Get 7.1 Notes
Agenda :
Water in the Air
- Water Cycle
- Humidity
- Condensation
Standard : Analyze meteorological data to predict weather conditions.
WATER IN THE AIR
UNDERSTANDING WEATHER
7.1
WATER IN THE AIR
Think about it…
In your own words…what is weather?
Weather is……
 The condition of the atmosphere at a certain time and place
 The condition of the atmosphere is affected by amount
of water in the air
 To understand weather, you need to understand how
water cycles through Earth’s atmosphere!
THE WATER CYCLE
 Rain bump your neighbor and identify the 3 states of water
 Water in whatever form is constantly being recycled
through the water cycle.
 The water cycle is the continuous movement of water from
sources on Earth’s surface - such as lakes, oceans and plants
- into the air, onto and over land, into the ground, and back
to the surface.
THE WATER CYCLE
 Condensation occurs when water vapor cools and changes from
a gas to a liquid. Clouds form by this process.
 Evaporation occurs when liquid water changes into water vapor,
which is a gas.
 Precipitation occurs when the rain, snow, sleet, or hail falls from
the clouds onto Earth’s surface.
 Runoff is water, usually from precipitation, that flows across land
and collects in rivers, streams, and eventually the ocean.
What is the water cycle?
Rain bump another neighbor to answer…
HUMIDITY
 As water evaporates from lakes, oceans and plants, it becomes
water vapor - invisible moisture in the air
 The amount of water vapor in the air is humidity
 As water evaporates & becomes water vapor, humidity increases
 As temperature of air increases, air’s ability to hold water vapor
increases
RELATIVE HUMIDITY
 Relative humidity - the amount of water vapor in the air compared
with the maximum amount of water vapor that the air can hold at a
certain temperature
 Relative humidity is given as a percentage
 When air holds all the water that it can at a given temperature,
it is said to be saturated
 Saturated air has a relative humidity of 100%
RELATIVE HUMIDITY
 How can you discover the relative humidity of air
if it is NOT saturated?
 If you know the maximum amount of water vapor that air
can hold at a given temperature and the actual amount of
water vapor in the air, you can calculate the relative humidity.
 Check out page 185 for a math challenge!
 Demonstrate RH with sponges
FACTORS AFFECTING
RELATIVE HUMIDITY
 Two factors that affect relative humidity are:
amount of water vapor and temperature
 At constant temperature and pressure, as amount of water vapor in air
changes, the relative humidity changes
 More water vapor = higher relative humidity
 If amount of water vapor in the air stays the same but temperature changes,
the relative humidity changes
 Relative humidity decreases as temperature rises and increases as
temperature drops
MEASURING RELATIVE
HUMIDITY
 A psychrometer is an instrument that is used to measure relative humidity.
 Consists of two thermometers:
1. wet-bulb thermometer - covered with a damp cloth
2. dry-bulb thermometer
 Difference in temperature readings between the 2 thermometers
indicates the amount of water vapor in the air.
 The larger the difference between the 2 readings is, the less water vapor
the air contains and the lower the humidity
HOW DOES IT WORK?
• A wet-bulb thermometer works differently from a dry-bulb thermometer,
which measures only air temperature
• As air passes over wet-bulb, water in cloth evaporates, cloth cools
• If humidity is low, water will evaporate more quickly and temperature
reading on wet-bulb thermometer will drop
• If humidity is high, only a small amount of water will evaporate from the
cloth of the wet-bulb thermometer, and the change in temperature will
be small
CONDENSATION
 Have you ever seen water droplets form on the outside of a glass of ice
water? Where did those water droplets come from?
 The water came from the surrounding air, and droplets formed as a result of
condensation.
 Condensation is the process by which a gas, such as water vapor,
becomes a liquid
 The air has to be saturated before condensation can occur. - Thinking back to
relative humidity, do you remember what the % must be for saturation take
place? Write the answer on the side of your notes.
DID YOU WRITE….100%
 Before Condensation can occur, the air must be saturated, which means
that the air must have a relative humidity of 100%
 Condensation occurs when saturated air cools
 Air can become saturated when water vapor is added to the air through
evaporation. Air can also become saturated when it cools to its dew point
 The dew point is the temperature at which a gas condenses into a liquid
 The ice in the glass of water causes the air surrounding the glass to cool
to its dew point
 Before water vapor can condense, it must have a surface to condense on
like the outside of the glass
PUTTING IT TOGETHER
 What is weather?
 What are the 4 stages of the water cycle?
 Humidity is the amount of _____________in the air.
 When the temperature of the air cools to its___________,
the air has reached saturation & condensation occurs.
WATER CYCLE WRITING
You will write a story from the point of view of a water droplet
traveling through the complete water cycle.
You must describe your adventure through ALL four stages of water cycle:
Evaporation
Condensation
Precipitation
Runoff
Be creative! Your writing needs to show that you understand how water
continuously moves from sources on the Earth’s surface, such as lakes, oceans,
and plants – into the air, onto and over land, into the ground, and back to the
surface.
Length: 1-2 pages types or neatly written