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- Hi, I'm Lauren Vogelbaum,
and this is Brain Stuff.
Pop quiz.
I'm thinking of a substance.
Let's see if you can guess what it is.
In its pure form it's odorless, tasteless,
and nearly colorless.
It's in your food.
In fact, a lot of the
stuff you use everyday
either contains it or was
manufactured using it.
It's even in your body.
Can you guess what it is?
If you guessed water, then you're correct.
Water is one of the most
important substances on Earth,
as far as life goes, at least.
And it can do some weird stuff.
For example, it reaches a maximum density
at around four degrees Celsius,
and then becomes less
dense before it freezes.
And here's another weird thing.
Hot water can freeze
faster than cold water.
But why?
Okay, this is a very old question.
Rene Descartes thought about it
and Francis Bacon before him.
Aristotle pondered the mystery, too.
Today, we call the
phenomenon the Mpemba effect,
after a guy named Erasto Mpemba,
who first observed the effect on ice cream
when he was just 13 years old.
His teacher, for the
record, laughed at him,
but who's laughing now?
It turns out Erasto
was onto something big,
and teams of experts would
spend the next few decades
trying to explain why
water behaves this way.
Scientists around the world
cooked up dozens of theories,
and none of them were able
to completely explain the process.
But, as of 2013, that may have changed.
A research assistant at the
University of Zagreb in Croatia
claims that convection
currents in warm water
cause it to cool more rapidly.
And the Royal Society of
Chemistry agrees with him.
They actually gave the
guy a thousand pound prize
for his experiments.
But he's not the only
contender for a solution.
A team of physicists
at the Nanyang Technological
University in Singapore
took the question to a much smaller level.
They claim the answer lies in the bonding.
Not, you know, hanging out with friends,
playing increasingly inappropriate games
of Cards Against Humanity kind of bonding,
but molecular bonding.
You see, every water molecule is made
of two hydrogen atoms bonded
to a single atom of oxygen.
These are covalent bonds,
which means that they share
electrons between one another.
It's a chemical bond.
Separate water molecules, however,
are bound to their neighbors
by weaker hydrogen bonds,
which occur when a hydrogen
atom from one water molecule
is close to the oxygen atom
of another water molecule.
This is an electro-magnetic attraction,
and it's what gives water
some of its really weird properties,
like the unusually high boiling point
of 100 degrees Celsius,
a.k.a. 212 degrees Fahrenheit.
So, these scientists in Singapore argued
that the Mpemba effect
comes from an interaction
between the covalent bonds,
those inner-water molecule bonds,
and the hydrogen bonds
between different molecules.
Here's how they think it works.
When water molecules are close together,
their natural repulsion
causes the covalent bonds
to stretch and store energy.
As the water warms up,
it becomes less dense.
The hydrogen bonds stretch
as the molecules move further apart.
When these hydrogen bonds stretch,
they allow the covalent bonds to shrink
and release their energy.
This is equivalent to cooling.
So, according to the Nanyang theory,
hot water is essentially able
to release energy faster,
leading to a quicker freeze.
Now, it's important to
note, at this point,
that the work hasn't been peer-reviewed,
so this is not a sure thing yet.
But even if it's just
a contributing factor,
that's a really promising
lead to a question
that has puzzled humanity
for some 2,500 years.
So, that should just about
wrap up this question.
If you have enjoyed this video,
then please like or subscribe,
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and/or one of my co-hosts,
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It is at brainstuffshow.com.
Go check it out, and we'll
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