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Free online chemistry lesson for elementary school, middle school and high school.
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Mechanics lessons
Water on Earth
Changes of state in the nature: the water cycle
Water in human body
Test for water
Properties of water in different states
States of matter
States of matter and its changes
Boiling water
Water: freezing and melting
Changes of state: mass and volume
Molecules in different states of matter

Mixtures and solutions
Heterogeneous mixtures
Homogeneous mixtures
Vaporization of water
Dissolving a solid in water
Conservation of mass on dissolving
Miscibility in water

Mass and volume
Volume and its units
Measuring volume with a graduated cylinder
Mass and its units
Measuring the mass of a liquid
Mass of a liter of water
Volumetric mass density
Air and atmosphere
Earth's atmosphere protect us
Threats to the Earth's atmosphere
Composition of air
Air and life
Atoms and molecules
Molecules in mixtures and pure substances
Molecules and states of matter
Composition of molecules
Constituents of the atoms
The electrical neutrality of the atom

Basics of combustion
The combustion of carbon
The combustion of butane
Atoms and chemical reactions
Chemical reactions
Chemical equations
Law of conservation of mass
Chemical synthesis

Most common metals

How to distinguish metals ?

Corrosion of metals

Electrical conductivity of solid materials

Electrons and free electrons

Electric current in metals
The conductivity of aqueous solutions
Aqueous solutions and ions
The direction of movement of ions
Formation of ions
Tests for ions
Acidic and basic solutions
pH of aqueous solutions
Ions in acidic and basic solutions
Dilution of acids and bases
Composition of hydrochloric acid
Chemical reaction between iron and hydrochloric acid

Electrochemical cells and chemical energy
Chemical reaction beteween a copper sulphate solution and zinc
Copper sulfate and zinc battery
Basics of electrochemical cell



The water cycle


The essential about the water cycle

The water cycle explained

Water is present in nature under many different and temporary forms. All changes that may affect water in nature contribute to the water cycle. 

Water cycle diagram
The water cycle in nature
( diagram: an example of water cycle )

Steps of water cycle
Step 1: Under the influence of Sun and winds, the water from oceans, seas (and all the reserves of liquid water in the open air) undergoes a vaporization.
Note: All trees and plants also produce water vapor (this phenomenon is called evapotranspiration).

Step  2: Water vapor, invisible to the naked eye, rises into the atmosphere.

Step  3: In contact with a layer of cold air, water vapor becomes liquid and forms clouds made ​​of tiny water droplets.

Step  4: Pushed by the winds, clouds reach the inland.

Step  5: When the droplets that form the clouds become too heavy they finally fall and form a rain.

Step  6: Once on the ground, the water from precipitations may flows or it can also penetrate the soil (it infiltrates).

Step  7: At high altitudes, temperatures can become very low. The droplets that form clouds solidify to form ice crystals.

Step  8: When ice crystals combine to form heavier snowflakes, they fall and form some snow.

Step  9: If the snow falls on mountains high enough it can feed a glacier or forms a snowpack.

Step 10: Fusion of snow and glaciers gives birth to rivers that may join a lake.

Step 11: The groundwater fed by rainwater that infiltrates the ground may spray out at the surface as source that give birth to a river.

Step 12: The rivers flow into other rivers and finally reach a sea or an ocean.


Learn more about water cycle

Kidszone: the water cycle explained to kids with worksheet to download.

The water cycle - Water science for school: The water cycle ( also called hydrologic cycle ) explained with a beautiful and detailed diagram.

Flash water cycle: animated flash water cycle that explains vapor, clouds, rain and water storage.

Earthguide - water cycle diagram: another animated diagram that shows how water moves in nature and its differents forms

South east water - water cycle game: an interactive game to learn different steps of water cycle