The water cycle

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Overview of the Water Cycle

The water cycle is a nonstop recycling process with no starting or ending point.
Water constantly moves between living organisms (e.g., plants) and non-living things (e.g., clouds, rivers, oceans).
It involves oceans, lakes, land surfaces, and the atmosphere.
Water molecules can cycle through almost anywhere on Earth due to water's properties.

A hand-drawn water cycle diagram showing evaporation from the ocean and from mountain streams, precipitation falling as rain over the hills, and freezing, melting and runoff on the mountainside.

Key Processes in the Water Cycle

Evaporation: Liquid water changes to gas (water vapor) when it gains energy from the Sun.
Condensation: Water vapor loses energy, becomes denser, and changes to tiny liquid droplets, forming clouds.
Precipitation: Cloud droplets collide and grow; when heavy enough, they fall as rain, snow, sleet, or hail.
Runoff: Precipitation that flows over land into streams and rivers, eventually returning to oceans.
Infiltration: Water seeping into the ground.
Transpiration (or evapotranspiration): Water evaporates from plant leaves, returning water to the atmosphere.

The USGS water cycle diagram, showing evaporation and evapotranspiration rising from the ocean and land, condensation and precipitation over the mountains, and runoff, infiltration and groundwater flow returning water underground and across the surface to the ocean.

Forces Driving the Water Cycle

Solar Energy: The Sun provides the energy that drives evaporation and the water cycle.
Density: Heated air expands, becomes less dense, and rises; cooler, denser air sinks.
Gravity: Pulls denser air downward, causing rising air; also causes water to flow downhill as runoff.
Energy transfer: Condensation releases energy to surrounding air, heating it and causing updrafts that keep cloud droplets aloft.

Earth's Water Reservoirs

Oceans: Store about 97% of Earth's water.
Atmosphere: Holds water vapor, clouds, and precipitation.
Streams and Lakes: Freshwater bodies fed by runoff and melting snow/ice.
Soil: Holds soil moisture important for plant growth.
Groundwater: Water stored in aquifers (porous rock layers) for centuries.
Biosphere: Water stored in plants and animals; plants release water vapor via transpiration.

The USGS water cycle diagram, showing the ocean, groundwater storage, freshwater and plant-uptake reservoirs where water is held as it moves through the cycle.

Water Cycle and States of Matter

Water exists in solid (ice, snow), liquid (rain, lakes), and gas (water vapor) states in the cycle.
The hydrosphere includes all water in all states of matter.
Condensation can form liquid droplets; if cold enough, water vapor can freeze into ice crystals.

Water Cycle and Living Things

Plants absorb water through roots and release it via transpiration.
Animals depend on water for survival and are part of the biosphere reservoir.
Aquatic habitats include freshwater (streams, lakes) and saltwater (oceans, seas).
A small percentage of Earth's water is freshwater; most is saltwater.

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Soal latihan

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1.What is the process by which water changes from a liquid to a gas?
Easy
- ACondensation
- BEvaporation
- CPrecipitation
- DTranspiration
2.Which of the following is the process by which water vapor changes into tiny droplets of liquid water?
Easy
- AEvaporation
- BCondensation
- CPrecipitation
- DRunoff
3.The water cycle has a starting point and an ending point.
Easy
True or false?
4.Transpiration is the process by which plants release water vapor into the atmosphere.
Easy
True or false?
5.Match each water cycle process with its correct description.
Easy
- Transpiration
- Condensation
- Precipitation
- Water vapor changes to liquid droplets
- Water falls from clouds to the ground
- Water vapor released from plant leaves
6.Put the following steps of the water cycle in the correct order, starting with evaporation from the ocean.
Medium
- Condensation forms clouds
- Precipitation falls to the ground
- Evaporation of ocean water
- Runoff flows back to the ocean
7.Which of the following are processes that return water to the atmosphere? (Select all that apply)
Easy
- AEvaporation
- BCondensation
- CTranspiration
- DPrecipitation
- ERunoff
8.The Sun is the primary source of energy that drives the water cycle.
Easy
True or false?

Soal lainnya

9.Why does warm, moist air rise in the atmosphere?
Medium
- AIt is denser than cold air.
- BIt is less dense than cold air.
- CIt has more mass than cold air.
- DIt is pushed by gravity.
10.What force causes water to flow downhill along the surface?
Medium
- ASolar energy
- BDensity
- CGravity
- DCondensation
11.In the water cycle, what happens to the energy released when water vapor condenses?
Medium
- AIt is lost to space.
- BIt is absorbed by the surrounding air molecules, increasing their motion.
- CIt is used to evaporate more water.
- DIt is stored in the water droplets.
12.Most of Earth's water is freshwater.
Easy
True or false?
13.A student observes a puddle after a rainstorm. Over time, the puddle disappears even though the temperature is below the boiling point of water. Which process is primarily responsible for the disappearance of the puddle?
Medium
- ACondensation
- BEvaporation
- CPrecipitation
- DInfiltration
14.A water droplet in a cloud becomes large enough to fall as rain. What causes this droplet to fall?
Medium
- AThe droplet becomes less dense than the air
- BThe droplet's weight is no longer supported by the upward force from rising air
- CThe droplet freezes into ice
- DThe droplet is pulled upward by the wind
15.A student sets up a simple experiment: a dish of water is placed on a windowsill in sunlight, and another identical dish is placed in a shaded cupboard. After a week, the water level in the sunny dish is much lower. What is the best explanation for this difference?
Medium
- AThe water in the sunny dish evaporated faster because it received more energy from the Sun.
- BThe water in the cupboard condensed.
- CThe water in the sunny dish infiltrated into the dish.
- DThe water in the cupboard was absorbed by the dish.
16.A student models the water cycle in a closed terrarium. The terrarium is sealed and placed in a sunny window. Water evaporates from the soil, condenses on the glass, and falls back as precipitation. Which of the following best describes the energy transformations that occur in this model?
Hard
- ALight energy from the Sun is absorbed by the water and soil, increasing evaporation; when water vapor condenses, thermal energy is released to the surroundings.
- BGravitational potential energy is converted to kinetic energy as water falls, and then to thermal energy during evaporation.
- CChemical energy in the soil is converted to thermal energy, driving evaporation and condensation.
- DThe water cycle in the terrarium is driven by the temperature difference between the soil and the glass, not by solar energy.
17.In a closed terrarium model of the water cycle, the total amount of water in the terrarium remains constant over time.
Easy
True or false?
18.A student is investigating the effect of wind on evaporation. She places two identical wet sponges in two different locations: one in a breezy area and one in a calm area. Which of the following factors should she keep constant to ensure a fair test? (Select all that apply)
Medium
- AThe temperature of the surroundings
- BThe amount of water initially in each sponge
- CThe type of sponge
- DThe amount of wind
- EThe time allowed for evaporation
19.Match each experimental setup to the water cycle process it best models.
Medium
- A dish of water placed in sunlight
- A sealed bag with moist soil left in a warm place, with droplets forming on the inside
- Water flowing down a sloped tray into a container
- Evaporation
- Condensation
- Runoff
20.A student wants to measure the rate of transpiration from a plant. Which of the following methods would be the most direct way to measure this?
Medium
- APlace a clear plastic bag over a leafy branch and measure the amount of water that condenses inside over time.
- BWeigh the entire plant and pot at the beginning and end of the experiment, without covering any part.
- CMeasure the diameter of the stem before and after watering.
- DCount the number of leaves and estimate the rate based on leaf area.
21.A student places a glass of ice water on a table. After a while, water droplets form on the outside of the glass. Which process is responsible for the droplets forming?
Medium
- ACondensation of water vapor from the air onto the cold glass
- BEvaporation of water from the glass through the walls
- CTranspiration from the glass material
- DPrecipitation from the air inside the glass
22.Which process describes the movement of water into the ground?
Easy
- AInfiltration
- BRunoff
- CEvaporation
- DCondensation
23.Fill in the blank with the correct term.
Easy
The process by which water falls from the sky as rain, snow, sleet, or hail is called ____.
24.What is the name for any location where water is stored on Earth, such as oceans, clouds, or living things?
Easy
25.Approximately what percentage of Earth's water is stored in the oceans? (Enter a number)
Easy
26.Approximately what percentage of Earth's water is stored in the oceans?
Easy
- A50%
- B75%
- C97%
- D99%
27.Complete the sentence.
Easy
The process by which water changes from a liquid to a gas is called ____.
28.Complete the sentence with the correct term.
Easy
The process by which water vapor changes into tiny droplets of liquid water is called ____.
29.Name the three states of matter in which water can exist in the hydrosphere.
Easy
The three states of matter that water can be in are ____, ____, and ____.
30.In an experiment, a student measures that 50 mL of water evaporates from a container in 5 hours. What is the average rate of evaporation in mL per hour? (Enter a number)
Medium
31.Describe the pathway of a water molecule that evaporates from the ocean and eventually returns to the ocean. Include at least three processes.
Hard
32.A student claims that the water cycle is driven by both the Sun and gravity. Describe how these two forces work together in the water cycle, using specific processes.
Hard
33.The salt flats in Death Valley cover a large enclosed basin. Streams carry dissolved salts down into the basin, and the salts are left behind as mineral flats. Identify the water cycle process most directly responsible for leaving the salts behind, and explain how energy from the Sun drives that process.
Medium
34.The diagram shows a model of the water cycle with four labeled steps. Step W shows water rising from the ocean surface toward the clouds. Which change would most likely increase the movement of water during step W?
Medium
- AAn increase in absorption by the soil
- BAn increase in cloud cover
- CAn increase in precipitation
- DAn increase in solar radiation
35.Complete the sentences about water moving through the Great Lakes.
Easy
The rise in Great Lakes water levels each spring is mostly caused by ____, and the river water then flows downhill toward the ocean because of ____.

Catatan ulasan

## The Water Cycle (Hydrologic Cycle) The water cycle is the continuous movement of water on, above, and below Earth's surface, driven by **energy from the sun** and **gravity**. Water changes between liquid, solid (ice), and vapor phases as it moves through reservoirs (oceans, atmosphere, ice, groundwater). ### Key Processes - **Evaporation**: Liquid water → water vapor (gas). Absorbs heat (latent heat of vaporization). 86% of global evaporation comes from oceans. - **Transpiration**: Water vapor released from plants. - **Evapotranspiration**: Combined evaporation from soil and transpiration from plants. - **Condensation**: Water vapor → liquid water droplets (clouds, fog). Releases heat. - **Precipitation**: Water falls as rain, snow, hail, or sleet. - **Sublimation**: Ice/snow → water vapor directly. - **Infiltration**: Water soaks into the ground. - **Surface runoff**: Water flows over land into rivers, lakes, oceans. - **Groundwater flow**: Water moves underground; some emerges as springs or discharges into surface water. ### Reservoirs & Distribution - Oceans hold **97%** of Earth's water. - 78% of precipitation falls over oceans. - Freshwater is stored in ice caps, glaciers, lakes, rivers, and aquifers. ### Energy & Purification - Phase changes transfer heat: evaporation absorbs heat; condensation releases heat. - The cycle purifies water: evaporation leaves salts behind; condensation produces freshwater. - Water cycle transports heat from tropics to poles via ocean currents. ### Human Impacts - Deforestation, urbanization, groundwater extraction alter natural water flow. - Climate change intensifies the cycle, causing shifts in precipitation patterns, more extreme weather, and changes in rainfall timing. ### Key Formula/Concept - **Latent heat of vaporization**: Heat absorbed when water evaporates. - **Density**: Water vapor is less dense than air (lower molecular mass), so it rises. > Remember: The sun provides energy; gravity pulls water downhill and causes precipitation.

Evaporation: The process by which liquid water changes into water vapor (gas) due to heat from the sun; absorbs latent heat of vaporization.
Condensation: The transformation of water vapor into liquid water droplets, forming clouds or fog; releases heat.
Precipitation: Water falling from the atmosphere as rain, snow, hail, or sleet.
Transpiration: The release of water vapor from plants into the atmosphere.
Evapotranspiration: The combined process of evaporation from soil and transpiration from plants.
Sublimation: The direct change of ice or snow into water vapor without melting.
Infiltration: The process by which water on the ground surface enters the soil.
Surface runoff: Water flow over land surfaces, often into rivers and streams, eventually reaching oceans.
Groundwater: Water stored underground in aquifers; can discharge into surface water or be taken up by plants.
Latent heat of vaporization: The heat energy absorbed when water evaporates from liquid to vapor.
Advection: The movement of water vapor through the atmosphere, enabling precipitation over land.

Kartu flash

What drives the water cycle?

Energy from the sun and gravity drive the water cycle.

What are the main processes in the water cycle?

Evaporation, condensation, precipitation, and collection (including runoff and infiltration).

What is evaporation?

Evaporation is the process where liquid water changes into water vapor (gas) due to heat from the sun.

What is condensation?

Condensation is the process where water vapor cools and changes back into liquid water droplets, forming clouds or fog.

What is precipitation?

Precipitation is water falling from clouds as rain, snow, sleet, or hail.

What is transpiration?

Transpiration is the release of water vapor from plants into the atmosphere.

What is evapotranspiration?

Evapotranspiration is the combined process of evaporation from surfaces and transpiration from plants.

What is sublimation in the water cycle?

Sublimation is the direct change of ice or snow into water vapor without melting into liquid first.

What is infiltration?

Infiltration is the process where water on the ground surface soaks into the soil.

What is surface runoff?

Surface runoff is water that flows over land surfaces into streams, rivers, and oceans without infiltrating.

What is groundwater?

Groundwater is water stored underground in porous rock layers called aquifers.

What role does the ocean play in the water cycle?

The ocean holds 97% of Earth's water, provides 86% of global evaporation, and receives 78% of global precipitation.

How does the water cycle purify water?

Evaporation separates water molecules from salts and impurities, and condensation forms fresh water droplets.

What is advection?

Advection is the movement of water vapor through the atmosphere, allowing evaporated water to travel to other regions.

How does the water cycle transfer heat?

Evaporation absorbs heat (latent heat of vaporization), and condensation releases heat, helping transfer energy from tropics to poles.

What are aquifers?

Aquifers are underground layers of rock or sediment that store and transmit groundwater.

What is the hyporheic zone?

The hyporheic zone is the area where surface water and groundwater mix in riverbeds and floodplains.

How do human activities affect the water cycle?

Deforestation, urbanization, groundwater extraction, and climate change alter natural water cycle processes and patterns.

What is the latent heat of vaporization?

The latent heat of vaporization is the heat absorbed when water changes from liquid to vapor, cooling the environment.

Why do clouds form?

Water vapor rises, cools, and condenses into tiny droplets around particles, forming clouds.

What is fog?

Fog is condensation of water vapor close to the ground, forming a cloud at ground level.

How does the water cycle affect Earth's geology?

Flowing water causes weathering, erosion, and deposition, reshaping landforms and transporting minerals.

What percentage of Earth's water is in the ocean?

About 97% of Earth's water is in the ocean.

What is an atmospheric river?

An atmospheric river is a narrow corridor of concentrated water vapor in the atmosphere that transports large amounts of moisture.

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