Why ice floats

Ever heard of this saying, 'just the tip of the iceberg'? If yes, then you might also acknowledge that most of the people who often use it don’t even know, let alone understand, its origin.  For the meaning though, it is quite plain, it means, “just the surface part of the story, to mean there is more to it than just what has been said.” Understanding the origin of this popular saying will enable you to understand how the world’s majestic ship, the Titanic, met its dehumanizing end to the surprise of the many who had initially asserted the ship to be ‘unsinkable not even by God’. It only took simple physics and the ignorance of the ones in charge to see the ship tear down in the middle like a jaw upon another. For your information, ignorance is the mother of all atrocities. It all boils down to why ice floats.

When talking about floatation and sinking, we all know that there is a fluid involved. A fluid is a liquid or gas, e.g. Water or air. And then there is the substance of interest which can be of any nature, even a fluid itself. The substance may be solid like a stone or another fluid like paraffin. According to the father of floatation and sinking, Archimedes, an object floats if it’s less dense than the fluid in which it is immersed, and an object sinks if it is much denser than the fluid in which it is immersed. But what do you mean by dense? The word dense brings into mind density. Density is mass that exists for every unit volume. Unit volume means 1 measure of the volume e.g. 1cm^3 or 1m^3 or 1litre. Simply put, for every 1 unit of volume of a substance, there is a mass associated with it; e.g. for water, there is 1grams for every 1cm^3 hence the density of water is 1g/cm^3. A normal building stone has a density of almost 1.6g/cm^3 hence much denser than water and so the stone will sink in water. But ice is literally water in solid form, so how comes (solid) water floats in water?

While most substances are dense in their solid form, water reaches a maximum density at 4⁰C. As it cools further and freezes to ice it actually becomes less dense. This unique behaviour is due to hydrogen bonds. Well, what are bonds? You have most certainly used an adhesive like office glue or superglue at some point. If yes then that force that the glue provides between, let’s say, for example, your torn off paper and the original book or wherever you want to glue the paper to, is what we call a bond. So, what are hydrogen bonds?  A water molecule, famously called h-two-oh (H₂0), consists of two hydrogen atoms and one oxygen atom. The three particles are held tightly together by bonds. The bonds between the oxygen atom and each hydrogen atom are called covalent bonds. And in this state of oneness, hydrogen atoms tend to acquire a positive charge while the oxygen atom acquires the negative charge. Water molecules also attract each other (i.e. one H₂0 attracts another H₂0), this is due to the attraction of opposite charges between the hydrogen atoms on one H₂0 molecule and the oxygen atom on another neighbouring H₂0 molecule. These new kinds of bonds are called hydrogen bonds. As the water cools below 4⁰C the hydrogen bonds adjust to hold the negatively charged oxygen atoms apart, as like charges repel. This produces a crystal arrangement (lattice) unlike that in liquid water. So, it is given its own name, ice, though the elements involved are the same as those of liquid water. So, what?

From above, it became clear that the hydrogen bonds adjust to hold the negatively charged oxygen atoms apart. This obviously means a spread in structure, which to your understanding, means an increase in the amount of space occupied by the same amount of matter as before. But what is the amount of matter? Mass, right? And what do we call the amount of space occupied by matter? Volume, right? So, volume increases but mass stays the same. Look at the equations below.

 So, taking mass to be 10g and initial volume of liquid water to be 50cm^3

Since density=mass/volume; density=10g/50cm^3 =0.2g/cm^3

But if the water cools to ice, the volume increases to say 52cm^3 but the mass/ content stays the same at 10g. So, the new density=10g/52cm^3=0.1923g/cm^3. So, the density decreases. In a nutshell, ice is lighter than water. In fact, in reality, it is 9% less dense than water or we can also say ice takes up 9% more space than liquid water.


Just the tip

Another law of floatation and sinking states that a lighter object will sink to the level in which the submerged part displaces the fluid whose weight is equivalent to the object's weight. Since ice is lighter than liquid water, but with a higher volume, the ice will sink up to the level that it displaces a volume of water whose weight when measured will equate to the weight of the entire ice. Do the math and you will realize that it only requires about 91% of its body to be submerged into the water since it has a higher volume for every unit mass. So, the ice will float, with about 9% of its body emerged out of the water and approximately 91% of its body submerged underneath. Simply put, when you drive by an icy lake and seen ice floating, know that what you are seen above the water is only about 9% of the ice the remaining body of the ice, 91%, is submerged. So, you can guess how big that ice really is. Another important consequence of this is that lakes and rivers freeze from the bottom up, allowing fish to survive even when the surface of the lake has frozen over. If the ice sank the water would be displaced to the top and exposed to the colder temperature, forcing rivers and lakes to fill with ice and freeze, hence the death of the aquatic life. God is indeed a genius.

The Titanic’s captain and his control crew misjudged the size of the icebergs and this mistake was realized very late when the ship had already veered itself into large chunks of ice which merciless, as if a reptile’s jaws on a mammalian flesh, tore apart the ship’s deck. The majestic unsinkable man’s creation, set, plain in the eyes of men, how humongous the destruction of a humongous creation can be. Looks can be deceiving indeed, but if you chose to ignore the deceptive looks then you are likened to a fat bull walking itself to a trough of hay clearly set inside the butchery. Seek knowledge and the unclear shall be engraved clearly.