Unit 12: Earth's Water, Air, and Weather
The water and air constantly cycling around the planet, and the difference between the weather outside today and the climate of a whole region.
8 topics · 27 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
The Water Cycle
- How it worksHow does water evaporate into the sky, condense into clouds, and fall back down as rain in an endless cycle?
- Worked exampleFind how much of Earth's water is fresh water if the oceans hold about 97 percent of all the water on the planet.
- Common mistakeWhy doesn't water get created or destroyed as it moves through the water cycle?
- Going furtherWhat happens to how fast water cycles through a region when the temperature rises?
Your turn1 of 2
Find how much of Earth's water is fresh water if the oceans hold about 96 percent of all the water on the planet.Oceans
- How it worksHow do sunlight, temperature, and pressure change as you go from the ocean's surface down to its deepest trenches?
- Common mistakeWhy isn't the ocean the same temperature all the way down to the bottom?
- Going furtherWhat happens to sea level around the world as ocean water warms up and expands?
Your turn1 of 2
Why is the deep ocean pitch black even on the sunniest day at the surface?Weather vs. Climate
- How it worksHow does weather describe today's conditions while climate describes decades of averages for a whole region?
- Common mistakeWhy doesn't one really cold winter prove that the climate isn't actually warming overall?
- Going furtherWhat happens to a region's climate classification if its average rainfall shifts over 50 years?
Your turn1 of 2
Why can it snow on a spring day in a place that's still getting warmer on average every year?Clouds
- How it worksHow do tiny water droplets condensing around dust in the air clump together to form a visible cloud?
- Common mistakeWhy isn't a cloud made of water vapor, the invisible gas, rather than tiny liquid droplets?
- Going furtherWhat happens to a cloud's droplets when enough of them collide and merge to get too heavy to float?
Your turn1 of 2
A cloud is made of the same water as a puddle. Why does a cloud float in the sky instead of falling straight down like puddle water would?Storms
- How it worksHow does warm, moist air rising rapidly build the towering clouds that power a thunderstorm?
- How it worksWalk me through how warm ocean water feeds a hurricane and makes it spin faster the longer it stays over water.
- Common mistakeWhy doesn't lightning actually strike from the ground up, even though it looks instantaneous?
- Going furtherWhat happens to a hurricane's strength the moment it moves from open ocean onto land?
Your turn1 of 2
Why does a thunderstorm form on a hot, humid afternoon far more often than on a cool, dry one?The Atmosphere
- How it worksHow do the atmosphere's layers, from the troposphere up to space, differ in temperature and thickness?
- Worked exampleFind how much of the air you breathe is nitrogen if oxygen makes up about 21 percent and nitrogen makes up about 78 percent.
- Common mistakeWhy doesn't the atmosphere have a hard, sharp edge where air suddenly stops and space begins?
Your turn1 of 2
Find how much of the air you breathe is neither oxygen nor nitrogen if oxygen makes up about 21 percent and nitrogen makes up about 77 percent.Seasons
- How it worksHow does Earth's tilted axis aim sunlight more directly at one hemisphere for half of every orbit?
- Common mistakeWhy isn't Earth actually closer to the sun during summer than during winter?
- Going furtherWhat happens to the length of daylight hours as a hemisphere tilts from summer into winter?
- Ties togetherHow does Earth's tilt explain both the seasons and why the sun sits higher in the sky in summer?
Your turn1 of 2
Why is it summer in one hemisphere while it's winter in the other at the exact same moment?Day and Night
- How it worksHow does Earth spinning once every 24 hours create day on the side facing the sun and night on the side facing away?
- Worked exampleFind how many degrees Earth rotates in 6 hours if it spins 360 degrees every 24 hours.
- Common mistakeWhy isn't it actually the sun moving around Earth every day?
Your turn1 of 2
Find how many degrees Earth rotates in 16 hours if it spins 360 degrees every 24 hours.