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Weather Lab 6-8 / Week 05 / Tuesday
2/6
Week 05 · Water in the Air

Tuesday

The water cycle
// Evaporation, condensation and the dew point
⏱ about 20 min

Tuesday: The Water Cycle

Raven pins a big blank sheet to the lab wall and draws an ocean along the bottom. "One drop," she says. "Where does it go?"

Rocket grabs a marker. "Up! The Sun heats it and it evaporates." He draws a wobbly arrow into the sky.

"Then it cools and condenses into a cloud," Raven adds, drawing a puff. "Then what brings it down?"

Rocket pauses. "Wind?"

Nova circles the drawing slowly. "What pulls everything on Earth downward," she asks, "including you when you jump?"

"Gravity!" Rocket says, and draws rain. "Then it runs into a river and back to the ocean. And starts over."

Raven steps back. "Two engines," she says. "The Sun lifts the water. Gravity brings it home."

Two engines: the Sun and gravity

The U.S. Geological Survey describes the water cycle as where water is on Earth and how it moves.

Energy from the Sun and the force of gravity drive the movement. The Sun's energy evaporates liquid water into vapor.

Gravity makes water flow downhill on land. It also makes rain, snow and hail fall from clouds.

Water is stored in pools: the oceans, lakes, rivers, ice, soil, groundwater and the air. It moves between pools in steps called fluxes.

The Sun heats ocean, lake and river water
Water evaporates into vapor and rises
Rising air cools and vapor condenses into clouds
Gravity pulls rain and snow back down
Water runs off into rivers, soaks into the ground or is used by plants
Water returns to the ocean and the cycle repeats

Facts from the survey

The oceans store 96 percent of all the water on Earth.

About 90 percent of the moisture in the atmosphere evaporated from oceans, seas, lakes and rivers. Most of the rest came from plants.

Plants release water through tiny openings in their leaves. This is called transpiration, and it is evaporation from plants.

Once a water molecule evaporates, it spends about 10 days in the air before it falls again.

On average, the world receives about 38 and a half inches of precipitation a year over the oceans and land together.

StepDriven mainly byWhat changes
EvaporationEnergy from the SunLiquid water becomes vapor
TranspirationEnergy from the Sun, through plantsWater in leaves becomes vapor
CondensationCooling of rising airVapor becomes cloud droplets
PrecipitationGravityDrops and ice fall to the ground
RunoffGravityWater flows downhill to rivers and the ocean
FOLLOW THE DROP
  • Read the question.
  • Tap your answer.
Which two things drive the water cycle?
Where is most of Earth's water stored?
What is transpiration?
About how long does an evaporated water molecule stay in the air?
ONE DROP'S JOURNEY
  • ?The drop runs downhill in a river back to the ocean.
  • ?Gravity pulls the drop down as rain.
  • ?A drop evaporates and rises as vapor.
  • ?The Sun heats the ocean surface.
  • ?The rising air cools and the vapor condenses into a cloud droplet.
WHY THIS EXERCISEPutting the steps in order is the model this week's standard asks you to build.
StatementTrue or false?
Gravity makes rain fall.?
Most atmospheric moisture evaporated from the land.?
Plants put water vapor into the air.?
The oceans hold less than half of Earth's water.?
WHY THIS EXERCISEKnowing where water comes from and what moves it lets you explain any weather that involves water.
The force that pulls rain down is ____.
What percent of Earth's water is in the oceans? Type a number.
Evaporation from plants has its own name. Type it.
WHY THIS EXERCISELiving things are part of the water cycle too.
SUN OR GRAVITY?
  • Tap a card.
  • Then tap its spot.
1Evaporation
2Condensation
3Precipitation
4Runoff
Draw your own water cycle with an ocean, a mountain, a cloud, rain, a river and a plant. Label the Sun and gravity where they do their work.

Nice work following the drop. Tomorrow is Station Lab: you will pull water out of thin air with a cold glass.

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