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Weather & Water Final Exam Study Guide: Investigations 6 – 9
Answer Key
Investigation 6: Water in the Air
1. Define the following terms:

Evaporation –_when liquid water gains energy and changes to a gas

Condensation – when water vapor cools to the dew point and changes to liquid water

Relative Humidity – the current amount of water vapor in the air compared to the maximum amount
the air can hold at a certain temperature

Dew Point – the temperature at which water vapor in the air will become saturated and condense

Humidity – water vapor in the air

Saturation – when the relative humidity is 100% and the air is holding the max. amount of water vapor
that it can

Condensation Nucleus –_the surface on which water vapor condenses

Weather Balloon – weather tool that carries a radiosonde to collect weather data

Sounding – the data from a radisonde on a weather balloon
Relative Humidity Practice Problems:
2. Use the Humidity Calculation Chart (p. 32 in your notebook or p. 79 in the RB) to answer the question:
Dry Bulb 24°C
Wet Bulb 13 °C
Difference = 11
R.H.:___26%____
2. Dry Bulb 18°C
Wet Bulb 14°C
RH:___65%______
Difference = 4
3. If the air can hold a maximum of 45 g of water vapor, and there is currently 25 g of vapor in the air, what is
the relative humidity? (Show your work!)
(Current / maximum) * 100 = relative humidity
25/45 = .555 * 100 = 55.5%
4. Use the chart on page 31 of your notebook to answer the following questions. Show your work!
What is the relative humidity of a kg of air at 25 °C that contains:
(Hint: You need to first find the max. amount of water vapor the air can hold at that temp!)
a. 10 g of water vapor
At 25 C, the maximum amount it can hold is 20 g. So:
10g/20g * 100 = 50%
b. 15 g of water vapor
15 g/20 g * 100 = 75%
5. Why does sweating help keep a person cool? Explain in detail, and be sure to include:
a. changes in the state of the water
b. transfer of kinetic energy
When you sweat, your body releases water onto your skin. This water has less energy than your body heat, so
your body heat transfers to the sweat. As the sweat gains enough energy, it can change into water vapor
(evaporation) and go into the atmosphere. As the sweat leaves your skin, it takes that body heat energy with it,
cooling you off.
6. How does the kinetic energy change during evaporation?
The kinetic energy of the water increases.
7. How does the kinetic energy change during condensation?
The kinetic energy of the water decreases.
8. Why does condensation form on the outside of your glass of iced tea? Explain in detail and include:
a. the changes in the state of the water that are occurring
b. changes in kinetic energy (both inside and outside the glass)
The cold glass if iced tea has less energy than the surrounding air. As the air in contact with the glass transfers
energy to the glass, it cools. If the air cools enough to the dew point, it will condense on the outside of the glass
(surface).
9. What is the relationship between temperature and air pressure?
In a closed system (example: bottle), if you increase the pressure, the temperature increases.
10. If the amount of water vapor in the air stays the same, but the air temperature increases, what happens to
the relative humidity?
The relative humidity would decrease.
11. What do you think would happen to water vapor that condenses on a surface that has a temperature below
0°C? It freezes.
What is this type of dew called?
Frost
12. What is the difference between humidity and dew point?
Humidity is a measure of the amount of water vapor in the air. Dew point is the temperature at which water
vapor condenses & the R.H. would be 100% (air is saturated).
13. Circle the correct word from the pair to explain cloud formation.
Water vapor near the ground absorbs energy through (conduction/convection). The temperature
(increases/decreases) causing the density to (increase/decrease), therefore the water vapor (rises/sinks). As
the water vapor (rises/sinks), the temperature (increases/decreases), which causes the density to
(increase/decrease). The water vapor cools to its (dew point/relative humidity) and (evaporates/condenses),
forming liquid droplets of water. The liquid water needs (condensation nuclei / gas) on which to form. As
more and more water droplets (condense/evaporate), they form a visible cloud. As the water droplets continue
to grow larger, they can become too heavy and (precipitation/evaporation) occurs.
14. Below, draw a diagram to explain cloud formation.
See your notes.
Investigation 7: The Water Cycle
15. Define the following terms:

Water Cycle – the constant movement of water between Earth’s surface and the atmosphere.

Precipitation – when water droplets in a cloud become too heavy & fall to the ground

Percolation – when water filters through the soil

Transpiration – water released by plants through their stomata

Collection – when water gathers in specific areas such as lakes or ponds

Groundwater – water that flows like an underground river
16. What percentage of Earth is covered by water? 70-75%
17. Water Distribution on Earth:
2% is freshwater stored in icecaps and glaciers
1% is freshwater in a form usable by plants, animals, and people
97% is saltwater found in the oceans
18. If water is constantly being cycled and changing states, does the amount of water on Earth change?
No
**Be sure you know the possible stops of the water cycle! Study your water cycle diagram.
Investigation 8: Air Pressure and Wind
19. Define the following terms:

Atmospheric (air) pressure – the force of air pushing down on Earth’s surface

Isobars – lines on a weather map that connect locations with equal air pressure.

Wind – air that moves from areas of high pressure to low pressure
20. What is the relationship between air pressure and temperature?
Warm air creates areas of low pressure; cold air creates areas of high pressure
21. What is the relationship between pressure and volume?
As you increase the pressure, the volume decreases.
22. What is the relationship between pressure and density?
As you increase the pressure, the density increases.
23. Wind always flows from __high___ pressure to _____low______ pressure.
24. What does the distance between isobars indicate?
If the isobars are close together, this means the pressure is changing rapidly and the wind speed will be faster.
24. Explain, in detail, how wind forms. Be sure to include the following:
a.
b.
c.
d.
Differential heating (warm/cold areas)
Density differences
Pressure differences
Direction of wind
Different parts of the Earth heat up at different rates (differential heating). As air in one location heats up, the
air becomes less dense. As the air becomes less dense, it rises, creating at area of low pressure. In areas with
colder temperatures, that air is more dense and sinks, creating an area of high pressure. Because there are
now pressure differences, the air wants to balance out, therefore it moves from the areas of high pressure to the
areas of low pressure, creating wind.
For 25 – 28, draw the following local winds. In each, be sure to label the following: - check the FOSS website,
p. 48-49, or my drawings displayed in class. You can also check drawings from Inv. 7 & 8 Key
a.
b.
c.
d.
e.
day/night
warm/cold
rising/sinking air
high/low pressure
wind direction
25. Sea Breeze
26. Land Breeze
27. Mountain Breeze
28. Valley Breeze
Investigation 9: Weather and Climate
29. Define the following terms:

Stagnant Air – air that sits still over a source region

Source Region – the location over which stagnant air sits. The air will take on the characteristics of the
source region

Air Mass – a body of air that is uniform in temperature and humidity.

Front – the boundary between two different air masses

Warm Front – when a warm air mass moves in to replace a cold air mass.

Cold Front – when a cold air mass pushes a warm air mass out of the way

Greenhouse Effect – the ability of gases in our atmosphere (ex: carbon dioxide) to trap heat. This is a
good thing in the right amount, for it allows it to be warm enough on Earth for life to survive.

Global Warming – the increase in Earth’s average temperature
30. Identify and describe the following air masses:

cT – continental tropical – dry (over land) & warm

cP – continental polar – dry & cold

mT – maritime tropical – humid (over water) & warm

mP – maritime polar – humid & cold
31. When a cold air mass overtakes a warm air mass, what do you think happens to the warm air?
Because the warm air is less dense, the cold air wedges itself underneath and pushes the warm air, causing it to
rise & move out of the way.
32. If a cold air mass forms over Canada, what kind of air mass would it be? Continental polar
33. If a warm air mass forms over the Gulf of Mexico waters, what kind of air mass would it be?
Maritime Tropical
34. What is the difference between weather & climate?
Weather is the condition of Earth’s atmosphere at a specific time and place, while climate is the average
weather conditions over a long period of time.
35. Draw and label a warm front. Include the following: check your notes or p. 85 in the resource book
a. Front boundary line
b. Warm air location
c. Cold air location
d. Type of weather occurring
36. Draw and label a cold front. Include the following: check your notes or p. 85 in the resource book
a. Front boundary line
a.
b.
c.
d.
Front boundary line
Warm air location
Cold air location
Type of weather occurring