Why Is Water Slippery?

The questions that youngsters ask about science aren’t all the time simple to reply. Sometimes, their little brains can result in massive locations that adults overlook to discover. That is what impressed our series Science Question From A Toddler, which makes use of youngsters’ curiosity as a jumping-off level to research the scientific wonders that adults don’t even assume to ask about. The solutions are for adults, however they wouldn’t be doable with out the marvel that solely a toddler can convey. I would like the toddlers in your life to be part of it! Send me their science questions, and so they could function the inspiration for a column. And now, our toddler …

Why is water slippery?” — Oliver B., age Four

Car tires skid on a wet freeway. Your foot slides out from beneath you on a moist kitchen flooring. Sweaty palms lose their grip on the monkey bars on the park. Water is responsible — however we’re actually solely shocked by a slip due to how a lot friction there may be on the earth. Left to their very own units, objects naturally resist shifting in opposition to each other. At a microscopic degree, the whole lot — from palms to highways — is a mountain vary. But as unusual as that’s, water, one of many weirdest substances on Earth, is stranger nonetheless — it’s capable of make clean operators out of a tough world.

“When I take into consideration friction, I take into consideration taking the Rocky Mountains and smushing them on high of the Himalayas and dragging them throughout one another,” mentioned Jim Kakalios, professor of physics on the University of Minnesota. That’s what rubbing your palms collectively would appear like beneath a microscope. Even surfaces that seem clean to the bare eye have hidden crags that snag and sluggish motion. Add water to Kakalios’s analogy, although, and also you create a barrier — a buffer between the peaks, a filler stuffed into the valleys — that cancels out the tough topography. Water creates a smoothness that wasn’t there earlier than, permitting crashes and pratfalls to occur and thwarting recess gymnastics routines.

Even the slipperiness of ice is expounded to a skinny movie of liquid water on the floor, smoothing out the interplay between your toes and a frozen puddle, mentioned Philip Ball, science author and writer of “H2O: A Biography of Water.” The concept that ice is slippery due to water on its floor had been round for a very long time however wasn’t convincingly proved till 1987. And whereas that will appear to be a really very long time in the past to a Four-year-old, I guarantee you that this date is latest sufficient that many grown-ups are nonetheless coming to phrases with the concept the present 12 months just isn’t 1988. Turns out, water is a deeply unusual substance, and scientists say there are nonetheless issues left to be taught in regards to the molecule that covers 70 percent of planet Earth.

How bizarre is water? Unlike most liquids, it’s densest not at its freezing level, however at only a few levels hotter — a novel trick that enables lakes to type a lid of ice, rather than freezing solid, Kakalios mentioned. Water is secure for us to drink, but in addition so chemically reactive that it may’t be used to lubricate issues like engines due to the harm it would trigger contained in the machine. “We’re used to [water], however for those who lived in an alien world the place it was a novelty, you’d deal with it with care,” mentioned Chris Shepherd, trainer help supervisor for the Institute of Physics, a U.Okay.-based society of physicists and writer of educational analysis. Ball mentioned that it’s even bizarre that water is liquid in any respect, contemplating that when the opposite parts most much like oxygen hyperlink up with hydrogen what they type is a fuel. Carbon plus hydrogen makes methane, as an illustration. Nitrogen and hydrogen make ammonia.

Lots of this weirdness has to do with the chemical bonds that maintain atoms of hydrogen and oxygen collectively as H2O. Those connections are 10 occasions weaker than a typical chemical bond, Ball mentioned. But every molecule of water can type 4 of those weak bonds without delay, giving it the flexibility to type buildings that no different liquid can. “That signifies that when the water molecules are linked, they type a three-dimensional community,” Ball mentioned. “Because water does that, it makes it exhausting to speak in regards to the construction at a molecular degree. It’s virtually like one gigantic molecule that’s unfastened and floppy, without end making and breaking bonds. You have to speak about it as a dynamic factor that’s continually altering.”

The fixed change and weirdness means there are scientific mysteries about water that don’t have a solution but, Ball mentioned. Among them: There’s theoretical proof that liquid water would possibly really are available two completely different varieties — one among which is denser than the opposite. Ball described the distinction on the degree of molecular bonds. In the denser type of water, the molecules of H2O can be snuggled up, holding onto one another in a hug. In the less-dense type of water, in distinction, the water molecules can be holding palms, however not getting cuddly. A glass of the denser water would weigh greater than an equally full glass of the less-dense water.

Right now, these two types of water exist solely in laptop fashions. There’s proof to counsel that they may be actual, however not essentially proof that they do. Proving it will require establishing an experiment during which water is cooled previous the freezing level however with out being become ice. This unlikely sounding situation is feasible, Ball mentioned, as a result of ice has to have one thing to type crystals round, what Ball referred to as a nucleation website. That will be an impurity within the water or a spot the place the nonetheless water is instantly jostled, disrupting the molecules and giving them a possibility to lock up into the construction of ice. You can discover videos on YouTube of people that have “supercooled” water, turning it to ice immediately by pouring or bumping it. But, Ball mentioned, we don’t but have the technological capability to do that to the diploma essential to check the two-types-of-water concept.

If it is actual, although, it may assist clarify a number of the weirdness of water — together with why that slippery floor of ice can type on the highest of lakes and puddles, relatively than their being frozen by. That, and different anomalies, may simply be echoes of water’s secret twin life as two liquids in a single. It’s slippery like that.

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