Ice facts for kids

For water in its liquid state see Water

Ice in a basket

Crystals of ice on glass

Ice is the common name for frozen water. When water gets very cold, it turns into a solid form called ice. This happens at a temperature of 0° Celsius (which is 32° Fahrenheit or 273 kelvin).

You can easily make ice at home in a refrigerator or freezer. If you put water in a freezer and leave it, it will get cold enough to freeze. Using a copper or other metal container can make water freeze faster. Metals are good at moving heat, so they help the water cool down and freeze quicker than in a plastic ice tray.

How Water Becomes Ice

Water is special because it expands when it freezes into ice. This means ice takes up more space than the liquid water it came from. Because of this, ice is less dense than water, so it floats! Most other liquids become more dense when they cool down.

Water expands by about 9% when it turns into ice. This happens because the water molecules actually move farther apart when they form an ice crystal. This arrangement makes ice lighter than liquid water.

This expansion can cause problems. If water freezes in plumbing pipes, it can make them burst. Water in glass bottles can also make them explode when it freezes. When water freezes in cracks in rocks, it can expand enough to split even hard rocks apart. This is an important natural process that helps wear down mountains and turn rock into soil.

When most materials are cooled, their molecules vibrate less and pack closer together. When they reach their freezing point, these molecules usually form a crystal-like solid. Some materials, like glass, don't form crystals but become very stiff liquids that seem solid. Only Helium won't freeze, but other liquids like cooking oil or petrol freeze at temperatures most people don't experience.

Salt Water and Ice

Salt water needs to be much colder than pure water to freeze. The ice that forms from salt water has much less salt in it than the original water. This salty ice is also not as strong as ice made from pure water.

Spreading salt on ice can make it melt, as long as it's not too cold. The salt starts to dissolve the ice, forming a salty water mixture called brine. This brine isn't cold enough to stay frozen at the same temperature, so the ice melts.

Where Ice is Found on Earth

Because ice floats, even large bodies of water like some oceans only freeze on their surface. Most lakes never freeze all the way to the bottom. Even very cold oceans, like the Arctic Ocean, only freeze on top. This allows the liquid ocean water below to keep moving.

This is very important for Earth's climate. It helps spread heat around the planet, making temperatures less extreme. If ice sank instead of floated, oceans would fill up with ice from the bottom and stay solid. A solid ocean couldn't move heat around. But because ice floats on the surface, the water underneath can keep circulating, and the surface ice can easily melt when it gets warmer. Antarctica holds most of the world's ice.

Earth's Ice Ages

Earth's climate is always changing. When it gets very cold for a long time, it's called an ice age. During ice ages, huge parts of the Earth are covered in ice, snow, and glaciers. The reasons for ice ages are quite complex.

Currently, Global warming is affecting Earth's ice resources. The causes of global warming are also very complex and are being studied by scientists.

Dry Ice

Dry ice when put in water

There's also something called 'dry ice'. This is frozen carbon dioxide, not water. When dry ice is exposed to normal air, it turns directly into carbon dioxide gas. This gas has no smell or color.

The gas is so cold that when it mixes with air, it cools the water vapor in the air. This creates a fog that looks like thick white smoke. Dry ice is often used in the theatre to create fake fog or smoke effects.

Images for kids

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  The three-dimensional crystal structure of H₂O ice Ih (c) is composed of bases of H₂O ice molecules (b) located on lattice points within the two-dimensional hexagonal space lattice (a).

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  An alternative formulation of the phase diagram for certain ices and other phases of water

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  Frozen waterfall in southeast New York

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  Feather ice on the plateau near Alta, Norway. The crystals form at temperatures below −30 °C (−22 °F).

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  Ice on deciduous tree after freezing rain

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  A small frozen rivulet

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  Ice formation on exterior of vehicle windshield

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  An accumulation of ice pellets

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  A large hailstone, about 6 cm (2.4 in) in diameter

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  Snowflakes by Wilson Bentley, 1902.

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  Harvesting ice on Lake St. Clair in Michigan, c. 1905

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  Layout of a late 19th-Century ice factory

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  Loss of control on ice by an articulated bus

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  Channel through ice for ship traffic on Lake Huron with ice breakers in background

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  Rime ice on the leading edge of an aircraft wing, partially released by the black pneumatic boot.

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  Skating fun by 17th century Dutch painter Hendrick Avercamp

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  Ice pier during 1983 cargo operations. McMurdo Station, Antarctica

See also

In Spanish: Hielo para niños