We all know that objects that float on water have less density than the body of water. Weight is not an issue because ships and tankers have floated on oceans for many years. However, in the northern part of the world, we often see icebergs floating in the water without sinking, or even melting back into the water. How does this happen? Why does ice float?

Ice is simply water turned solid through exposure to very, very low temperatures. In fact, water forms into ice when the temperature drops to zero degrees Celsius. In its solid state, water is compressed, its molecules tightly packed together.

Despite its solid form, ice may have air pockets in it created during the freezing process. The air pockets help in making ice float even when it’s placed inside a glass water. To prevent air pockets from forming, water has to be heated first before it’s frozen. However, heating it up and cooling it down does not make the ice dense enough to sink like a rock in water. It still floats no matter how much surface area it occupies or how dense it becomes.

Floating Ice 1024x680 Why Does Ice Float?

Ice is 9% less dense

Most substances are most dense in their solid (frozen) state than in their liquid state. Water is different because of hydrogen bonding.

A water molecule is made from one oxygen atom and two hydrogen atoms. These atoms are strongly joined to each other with covalent bonds. Water molecules are also attracted to each other by weaker chemical bonds called hydrogen bonds between the positively-charged hydrogen atoms and the negatively-charged oxygen atoms of neighboring water molecules. As water cools below 4 degrees Celsius, the hydrogen bonds adjust to hold the negatively charged oxygen atoms apart. This produces a crystal lattice, which is commonly known as “ice.”

So, why does ice float? Like most things that float, ice floats because it is less dense than liquid water. Ice is about nine percent less dense. How is this so? Take a look at the molecular structures of ice and water. Ice has a diamond structure due to the hydrogen bonding. Water does not have such an orderly structure, but water molecules are squeezed close to one another because of the hydrogen bonding. As a result there is more space in between the molecules in ice than in water. This is the reason why ice, despite its solid form, floats.

Shouldn’t the ice be melting by now?

Icebergs in the Antartic region will not melt even when they are floating on water. The temperature above and below the water line keeps the ice in its solid state. Unlike the ice cubes in your glass of water, the icebergs are not exposed to environmental temperature higher than its internal temperature.

When the climate in the north changes, however, some of the icebergs, especially the smaller ones, float away and gardually melt. This event is heavily connected with Global Warming, which is a phenomenon when atmospheric changes in the Antartic region will increase environmental temperatures and melt the icebergs away. When this happens, the sea level will rise, and floods around the world will sink some cities under water. It is catastrophic enough when we imagine it, what more when it comes true?

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Categories: Physics & Chemistry

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