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Ice Floats On Water
Ashish
From giant icebergs to tiny
cubes, ice – the frozen form of water – always floats on its liquid form. Isn’t
that weird?
We’re not the only ones who
think it’s unusual; the entire world finds it rather surprising that a
solid should float on its liquid form.
Do a quick Google search and
you’ll find dozens of pages discussing this queer tendency of ice.
As it turns out, like everything else, there is
a scientific reason behind this phenomenon. But first off, let’s be clear about
what makes stuff sink or float.
The singular rule of thumb, when it comes to
the ability of an object to float in water (or any other liquid),
concerns the density of the object in question.
Have you ever heard of Archimedes’ Principle?
Archimedes’ Principle states that for an object to float on
water, it must displace an equal amount of water.
In other words, you can say that the fate of an
object in a body of water is decided by Archimedes’ Principle.
It’s common knowledge that solid objects have
more density than their liquid counterparts.
Chemically, this makes sense too. Molecules are
more closely bound with one another in a well-defined manner in a solid, which
makes them rigid and gives them more weight.
All common substances that we see and observe
in daily life follow this basic principle: solid objects are denser and
have more weight than liquids.
Given that, why does ice – which is a
solid – float on water? Shouldn’t it sink, as a solid, and according to
general convention, also have more density?
A Little Water Info
Water is a wonderful liquid, and full of
unusual behaviors and chemical structures, which is why it presents an
interesting exception to the general behavior of solids floating over their
liquid forms.
If you keep cooling a liquid, its density
continues to increase until it becomes solid, where it attains
maximum density.
However, in the case of water, this trend is
slightly different, which is the root cause of this whole discussion.
Water’s density increases as you continue to
cool it; but opposed to other liquids, which have their highest density when
they freeze, water achieves maximum density when its temperature reaches 4
degrees Celsius (39.2 Degrees Fahrenheit).
If you continue to cool water past 4 degrees
Celsius, its density starts to plummet (you can see this in the graph).
At zero degrees, i.e., the temperature at which
water turns into ice, the density of water is actually quite low.
It turns out that ice has a lower density than
water, and any object that has a lower density than the liquid form on which it’s
kept (in this case, water) will be able to float!
But why is the density of ice less than water?
To answer that, you’ll have to look at the
chemical structure of water.
The negatively-charged oxygen atoms bind
strongly with hydrogen atoms, forming a strong hydrogen bond.
When a liquid is cooled, more and more
molecules are brought closer together and need to be accommodated in a
smaller area. This gives most solids more density than their liquid form.
However, in the case of water, the
negatively-charged oxygen atoms repel each other (when brought together in a
smaller space) to prevent the ice from becoming any denser.
This is the reason that density actually
decreases as temperature continues to fall below 4 degrees Celsius.
Ashish is a Science graduate (Bachelor of Science) from Punjabi
University (India). He spends a lot of time watching movies, and an awful lot
more time discussing them. He likes Harry Potter and the Avengers, and obsesses
over how thoroughly Science dictates every aspect of life… in this universe, at
least.
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A water molecule is made of two hydrogen atoms
and one oxygen atom
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A graph showing how density varies with changing temperature |
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