A surprising twist on what makes ice so slippery

Some road conditions are worse than others when driving in the winter.
Published: Dec. 10, 2020 at 11:28 AM AKST
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ANCHORAGE, Alaska (KTUU) - It’s safe to say that we encounter some strange and unusual things in this world, but one of the more unusual substances is something we encounter every day.


It’s the only natural substance in this world that can be found in all three states at once: liquid, solid and gas. Think about it, you’re sitting in a hot tub (liquid), surrounded by steam (gas) and drinking a nice cold beverage topped off with ice (solid). It’s really strange when you think about it.

That’s not the only rule that water breaks, as it can dissolve practically anything, dubbing it a universal solvent. It has a high surface tension, allowing some insects to walk right on top of water. Its solid-state floats in its liquid state. And arguably the coolest, that being hot water freezes faster than cold water. Try it if you have some time!

All of this can be explained due to the chemical structure of water. We take it for granted each day, but when you really get down to the science of water, it’s amazing at the things you can learn.

Take for instance water in its frozen state. We learn at a young age that water freezes at 32 degrees, which leads many of us to drive more cautiously on roads during the winter, especially following recent rain or snow. Water in its frozen state leads to slick conditions and we know that all too well. From skidding on the roads, to slipping on the sidewalk, and falling when ice skating. We encounter this very frequently during the winter months in Alaska.

This leads to the next strange thing about water, in that it’s actually the most dangerous to drive when temperatures are several degrees below freezing. To begin, ice itself isn’t slippery at all. Try telling that to someone and they’ll look at you like you’re crazy.

Ice isn’t slippery because it’s a solid. However, all ice when exerted under pressure creates a thin filament of liquid water that leads to us slipping. This is due to the molecular structure of water as it freezes. Unlike most substances, the molecules of water move farther apart when exposed to colder temperatures. This leads to water expanding (as opposed to other substances, which shrink at colder temperatures). It’s not fully understood just what causes ice to become slippery, but a popular theory that dates back to the late 1800s has to do with pressure. As you step, drive, or skate over ice, you are exerting pressure and friction on the solid, which pushes the molecules back together causing a thin layer of water to develop on the ice, thereby creating the perfect environment for slippage.

A team of researchers released new data in 2018 about the molecular components of water and just why its solid-state becomes slippery. In the report, the team found that there are two types of water molecules that exist on the surface of the ice. One being water molecules that are stuck to the ice and bound by three hydrogen bonds and mobile water molecules that are bound by only two hydrogen bonds. It’s the latter that continuously rolls over ice like tiny balls. This essentially translates to your tires sliding on microscopic tiny balls when traveling on ice.

So what is the ideal temperature for maximum slippage?

The team concluded that the friction on ice, which is directly correlated to its mobility is -7-degrees Celsius (roughly 20-degrees Fahrenheit). Anything below that temperature makes it extremely more difficult for weaker bonds to be broken and become mobile.

Interestingly enough, we already knew this without realizing it. Go to your nearest skating rink and you’ll find that the temperature is kept roughly around 20-degrees to allow for the fastest skating time.

So the next time your outside driving in icy conditions and the air temperature is hovering near 20-degrees, remember just how unusual the most abundant substance on Earth is and drive cautiously.

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