Welcome to brain stuff from How Stuff Works. Hey, I'm Christian Saga and this is brain stuff pop quiz. I'm thinking of a substance. Let's see if you can guess what it is. And it's pure form. It's odorless, tasteless, and nearly colorless. It's in your food. In fact, a lot of the stuff you use every day 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 strange thing. Hot water can freeze faster than cold water. But why, Okay, this is a very old question. In fact, Renee Descartes thought about it, and Francis Bacon before him,
Aristotle pondered the mystery too. Today we call this phenomenon the Impemba effect, after a guy named Erasto Impemba, who first observed the effect on ice cream when he was just thirteen years old. His teacher, for the record, laughed at him, Well who's laughing now? Turns out Rasto 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 were able to completely explain the process. But as 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 Non Young Technological University in Singapore took
the question to a much smaller level. They claim that the answer lies in the bonding. Not you know, hanging out with friends type bonding, but molecular bonding two kinds actually. 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.
This is a chemical bond. Separate water molecules 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 electromagnetic attraction and it's what gives water some of its strange abilities, like it's unusually high boiling point of one hundred degrees celsius that's two hundred and twelve degrees fahrenheit.
So these scientists in Singapore argue that the Impemba effect comes from an interaction between the covalent bonds, you know, the 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 non Young theory, hot water is essentially able to release energy faster, leading to a quicker freeze. It's important to note that at this point that work hasn't been peer reviewed, so it's not a sure thing yet, but even if it's just a contributing factor, it's a promising lead to a
question that's puzzled humanity for some twenty hundred years. Check out the brain stuff channel on YouTube, and for more on this and thousands of other topics, visit how stuff works dot com.