Students who demonstrate understanding can: Develop a model to describe the cycling of water through Earth's systems driven by energy from the sun and the force of gravity.
Clarification statement: Emphasis is on the ways water changes its state as it moves through the multiple pathways of the hydrologic cycle. Examples of models can be conceptual or physical.
Assessment boundary: A quantitative understanding of the latent heats of vaporization and fusion is not assessed.
Official wording from the Next Generation Science Standards (NGSS Lead States, 2013). NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the NGSS were involved in the production of this page, and they do not endorse it. View on nextgenscience.org
A raindrop falling on a mountain might soak into the ground, flow into a river, be taken up by a tree, freeze into a glacier for a thousand years, or evaporate the very next day. Middle school students model the many pathways water can take through the atmosphere, land, oceans and living things, and identify the two drivers of the system: energy from the sun and the pull of gravity.
Sunlight supplies the energy that evaporates water from oceans, lakes and soil and powers transpiration from plants. As water vapor rises and cools, it condenses into the droplets that form clouds; when droplets or ice crystals grow heavy enough, gravity brings them down as precipitation. Gravity also drives runoff downhill into rivers and pulls water down through soil into groundwater. At each step water changes state, and those changes involve energy being absorbed or released.
Models can be diagrams or physical setups such as a sealed bag on a sunny window. A quantitative treatment of latent heat is outside the expectation.
Water vapor is an invisible gas. Clouds are tiny droplets of liquid water or ice crystals that formed when vapor cooled and condensed.
Diagrams with one circle hide most of the pathways. Water can spend years underground, centuries in an ice sheet, or days in the air.
Water evaporates at all ordinary temperatures, which is why puddles dry up on a cool day.
The sun provides energy for evaporation, but it does not pull water. Rising warm air carries water vapor upward.
A cold bottle taken from the refrigerator gets drops of water on the outside on a warm, humid day. Use the water cycle model to explain where the water came from and how this links to cloud formation.
Answer: The drops are water vapor from the air that condensed when cooled by the bottle, the same change of state that forms clouds.
A water cycle in a sealed bag taped to a sunny window, or a tray of warm water covered with plastic and topped with ice, lets students observe evaporation and condensation directly. Then challenge them to trace a single water molecule through different reservoirs, writing down the energy source or force behind each move.
Assessment items often ask students to complete or critique a water cycle model, or to identify the energy source or force behind a named process.
Original questions written for this standard. Choose an option or type your answer, then press Check. Every question has a worked explanation.
Answer: D) The sun
Sunlight supplies the energy that changes liquid water into water vapor.
Answer: A) Tiny drops of liquid water or ice crystals
Clouds form when water vapor condenses into tiny droplets or ice crystals.
Answer: B) Gravity
Gravity pulls precipitation down and causes runoff and rivers to flow downhill.
Answer: transpiration
Transpiration moves water from the soil, through the plant and out of the leaves as vapor.
Answer: condensation (also accepted: condensing)
Condensation is gas becoming liquid; it happens when vapor cools.
Answer: A) In a deep ice sheet or deep groundwater
Water can remain locked in ice sheets or deep aquifers for thousands of years, compared with days in the air.
Develop a model using an example to describe ways the geosphere, biosphere, hydrosphere, and/or atmosphere interact.
Plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes.
A full lesson with slides, activities and an exit ticket on modeling the water cycle, pitched to grades 6-8 and editable in PowerPoint or Google Slides.
Make a lesson βA printable, differentiated worksheet on MS-ESS2-4 with an answer key, ready in about a minute.
Make a worksheet βTurn modeling the water cycle into a quiz students answer online that marks itself, with a class summary for you.
Build a test βEnergy from the sun and the force of gravity. The sun drives evaporation and transpiration; gravity drives precipitation, runoff and infiltration.
No. A quantitative understanding of the latent heats of vaporization and fusion is not assessed.