Name:
ANSWER KEY
Weather and Water
Investigation 7 Water in the Air
Study Guide
1. What happens when particles decrease in kinetic energy?
Particles slow down, collide less often
2. Clothes are hung out to dry. What happened to the water as the clothes
dried?
Energy from the warmer air is transferred to the wet clothes. Water
particles gain enough kinetic energy to evaporate into water vapor.
3. How does a water sample evaporate?
Evaporation occurs because of energy transfer. A water sample
must gain enough energy to evaporate.
4. What is the difference between water vapor and clouds?
Water vapor is the gaseous state of water and is invisible. Clouds
are made up of tiny droplets of liquid water and are visible.
5. Write a paragraph to explain how clouds form.
Water vapor that has evaporated rises up in the atmosphere. As
water vapor rises, atmospheric temperature and pressure decrease.
Water vapor loses energy and condenses into liquid water on a
condensation nucleus (dust, dirt, salt, bacteria). More water vapor will
condense until the water droplet becomes a cloud droplet. Millions of
cloud droplets make up a cloud.
6. What happens when a sample of air drops in temperature to the dew point?
Water vapor will condense on surfaces as liquid water
7. What happens to gas particles in a closed container when you increase the
pressure?
Increasing pressure (particles are closer together and collide
more)→ increases kinetic energy (particles are moving faster) →
temperature increases (temperature is the measurement of the
average amount of kinetic energy)
8. Describe what happens to the water particles when a sample of water vapor
cools and condenses into liquid.
The sample of water will lose kinetic energy (slow down & collide
less), water vapor will condense into a liquid on a surface
9. Some students were outside, waiting for the school doors to open. It was a
very cold day, and the students were looking forward to being inside the warm
school building. When two of the students stepped inside the building, their
glasses fogged up, they couldn't see a thing! Choose true or false for each
statement.
The heat from the air inside the school is what condensed on the students'
glasses.
False - it is water vapor, not heat that condenses
The water vapor in the indoor air must have been warmer than the
students' glasses.
True - water vapor will only condense on cooler surfaces (water
vapor must have been warmer)
Energy transfers from water vapor in the air to the glasses.
True - the water vapor transferred energy to the cooler surface,
making it condense
When thermal energy is added to water particles in the air, particle motion
slows down and the particles spread apart.
False - adding thermal energy increases speed and makes particles
spread out
Energy transfer is what causes condensation to happen.
True
10. Define clouds:
Liquid water droplets in the atmosphere that are visible
11. Define: dew point
The temperature at which a sample of air will condense into liquid
on a surface/the point at which an air sample is completed
saturated and no more water can evaporate
12. Define: humidity
The amount of water vapor in the air
13. Define: transpiration
The continuous process in which water travels through plants and
releases it as water vapor
14. What is water vapor that condenses on a surface that has a temperature
below 0°C called?
Frost
15. Define: saturated
The condition in which the air contains all the water vapor possible
at that temperature
16. Define: condensation nuclei
Tiny suspended particles, either solid or liquid, upon which water
vapor can condense