Why Ice floats on Water?

Alex Williams
7 Min Read

We all know that ice floats on water. This phenomenon doesn’t just occur with small pieces of ice cubes, but giant icebergs on top of lakes and oceans too. Let us understand why and how ice floats on water!

1. What is Ice?

Ice is a state of solidified water. It reaches this stage through the process of freezing. Ice can be found in its frozen state in space as well. On Earth, ice is present in abundance in the polar regions i.e., the North and South poles. Ice also falls from clouds in the form of snowflakes during precipitation. Lakes, rivers, and ponds in places where the temperature reaches below freezing point can often be found covered in thick or thin sheets of ice on the surface.

2. What are Physical Properties of Ice?

Ice is a unique substance as its liquid form, water is denser than the solid form, ice. Occurring naturally, ice can be considered a mineral because it has an ordered structure. Also, it is in the form of crystalline inorganic solid. (See 9 Unique Properties of Chalk)

3. What are Molecular Arrangements of Ice & Water?

Water has a partially uniform structure as molecules of hydrogen are continuously being broken and formed. It happens because, at room temperature, water is not at rest. The molecular arrangement of water is tightly packed, i.e., one water molecule is bonded with 3.4 other molecules. On the other hand, ice floats because molecules of ice are not tightly packed, but have large spaces between each group instead. These groups are formed as each hydrogen molecule of ice is bonded to 4 other molecules. This difference in the molecular arrangement of ice and water contributes to the difference in their densities. (See Why do atoms form chemical bonds?)

4. How & Why Ice Floats on Water?

According to Archimedes’ principle, the explanation of why ice floats on water is that any object less dense than water will float. To put it in simple words, if an object is less dense than the other components in the mixture, then it’ll float. So, when an object floats, it displaces an amount of weight of fluid equal to its weight. To explain this theory, take an example of a couple of stones and a bucket full of water. When you toss a stone into the bucket of water, it immediately sinks, because the rock is denser than water. Hence, it displaces or pushes the water away.

As we know, solid objects are way denser and heavier than liquid. So, you might think that ice should sink into the liquid it is in. But, the shocking fact about ice is that it is 9% less dense than water itself. Additionally, the upward movement of the buoyant force helps make an object float. Therefore, it causes ice to float on top of the surface. (See The Mystery of Devils Kettle Waterfall)

5. What is Density of Ice and Water?

According to scientists, the density of water is 1.0 gram/cubic centimeter at 4 degrees Celsius (39.2 degrees Fahrenheit). In comparison to other materials or liquids, water is considered the densest of all and its density is affected by its temperature. The density of ice, however, is lesser than water. Ice has a density of about 0.931 grams/cubic centimeter. In other terms, the density of ice is about 9 percent lesser than that of water. (See How Hot is Lava in Fahrenheit?)

6. Why does Ice have Less Density?

When any liquid is cooled down, all of its molecules are brought in closer together, which requires them to be accommodated in a smaller space. This causes most of the solids to have more density compared to liquids, but there may be exceptions for the same, such as ice. Water consists of atoms, one being positively-charged hydrogen atoms, and the other being negatively-charged oxygen atoms. So, when the water cools down, the hydrogen bonds adjust themselves to hold the negatively-charged oxygen atoms apart, preventing the ice from becoming denser. (See How many ounces of water are in a 2-litre bottle?)

7. How do Icebergs Float on Water?

Ice is present in the form of glaciers in colder regions of the Earth, especially the polar regions. Antarctica and Greenland are covered with large sheets of ice. These sheets are known as continental glaciers. For an iceberg to float, its density must be less than water. To balance the density:

  • A large part of the iceberg gets submerged to a particular level below the surface.
  • Once the density of the iceberg reaches a level lower than density of water, it stops submerging.
  • The part of the iceberg above the sea level has a lesser density than water, and thus, it floats.

In this process, 80-90 percent of the iceberg is inside the water while only 10-20 percent is above it.

8. How Fast can Icebergs Float?

Icebergs can float in the water at a much faster speed than you might think. The range of iceberg drifting in water starts from 0.7 km/h to 3.6 km/h. Although speeds greater than 3.6 km per hour have also been recorded. Icebergs can float as the total area of the iceberg inside the water is approximately 20 to 30 percent bigger than its tip. They can take up to three or four years to melt in oceans. But until then, they continue to float like the iceberg which wrecked the Titanic. (See How Did the “Unsinkable” Titanic Sink?)

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