Unless we're slipping and sliding down the sidewalk or taking a drink, one doesn't spend much time thinking about the simple three-atom molecule which is all around us, but without it, life would not be possible. That little molecule is water. Water in any form is an amazing thing. And seemingly so simply. Two hydrogen atoms combine with one oxygen molecule using polar covalent bonds to form an unassuming but interesting molecule of water. But, it's the interaction of the individual atoms which make the molecule so unique.
Covalent bonds are ones in which the atoms 'share' their electrons. But, in some instances, the sharing isn't equal and one atom hugs the electrons closer, making the overall molecule slightly charged. In the case of water, the big oxygen atom is stronger and pulls the little hydrogen atom electrons closer to it. This causes the overall molecule to have a slight charge imbalance - the oxygen atom becomes a little more negative and the hydrogen slightly more positive. This difference in charge creates a 'polar' molecule (think about the positive and negative poles of a magnet or the positive and negative anodes of a battery).
But, it's one other interesting property of water which makes life possible. Let's switch gears and think about states of matter - you know: gas, liquid, solid. We all know something about the properties of each. We interact with all three everyday. The most important property when it comes to water is density. We know a gas is lighter than a liquid which is lighter than a solid. Thats true for almost all matter, except water. When most molecules transition from liquid to solid, the molecules move closer together, causing the solid to become more dense.
Not water, solid water or ice is less dense than liquid water. It's all about that little bit of charge, since water molecules are polar, each carries a slight charge. When liquid water freezes into ice something amazing happens. The slightly negatively charged oxygen atoms repel each other as the ice lattice forms - pushing the molecules apart - making the space between molecules bigger. This increases the lattice volume in solid form making it less dense allowing the ice to float on water. Had this not been the case and frozen ice was more dense than liquid water - all ponds, oceans and rivers would have frozen from the bottom up, pushing any evolving life to the surface.
All the chemistry aside we wouldn't have life on Earth without water. Geoscientists may argue about where the water on Earth came from - asteroids and comets striking the early planet, or concentrated from the primordial material which made up the planet, or from within Earth's mantle, or all three - liquid water has been around for at least 4.25billion years (reminder: the Earth is 4.55billion years old). Therefore, with a little twist of chemistry, life has had its required medium available throughout geologic time.
And where would us humans be? We wouldn't have had the last several weeks of athletic prowess demonstrated at the Milano-Cortina Games without frozen water. Whether sliding, skating or skiing - all the winter Olympic events took place on some form of ice. But not all frozen water is the same substance. All types of frozen water used in the Olympics are unique to the sport. In fact the frozen water is so specific to the sport - the Olympics employ 'ice meisters' to prepare and maintain the ice or snow surface for the athletes.
Each sport requires a different temperature, thickness and texture of frozen water:
Figure skating demands the softest or warmest ice -3degC (24-25degF) and the thickest surface to cushion the landing from jumps and prevent athletes from shattering the ice.
Short-track speed skating requires a colder harder, but thinner surface for high-speed sharp turns made by the exceptionally sharp thin skate blades -5.5degC (22degF)
Long-track speed skating requires the hardest, therefore coldest surface of all for maximum glide on each stroke of the blade -6-7degC (21degF)
Ice hockey requires an ultra tough, thick surface which is consistent across the entire rink -4.5-5degC (23degF). This allows the best slide on the puck and the ability of the skaters to make hard fast stops.
Sliding sports (luge, skeleton, bobsled) use a curved concrete track down which gravity throws the slider. The ice surface is made up of multiple thin layers of ice to create a hard smooth sliding surface.
Each of the skiing events want a different surface as well - remember many of these events were postponed or rescheduled because it had snowed over night? New unconsolidated snow needs to be removed to allow maximum speed to be generated during the event. For alpine skiing, all the new loose snow is pushed off the course and sometimes, water is sprayed on the snow surface to create a hardened layer. This allows a fast skiing surface into which edges can crave turns without grabbing and a course which will hold up throughout the runs. The same is true for free-style events.
Having the proper conditions, as well as, the right frozen water is a huge problem for the Olympic Committee as planet-wide warming decreases the number of possible venues for the winter games. It should also be noted, athletes do not like to ski on 'man-made' snow. The texture and grip is very different from the natural stuff which falls from the sky. This was one of the big negatives about the game in Beijing in 2022. The IOC will have their hands full with choosing locales for future games. They got lucky this year and northern Italy had great snow and cold. In 4 years the games will be in the French Alps. In 2030, let's hope La Niña doesn't re-establish. The games are scheduled to be held in Utah then. This year, just like Colorado, Utah has had a minimal snowfall of 48" versus a usual 350-500" and above freezing temperatures. Fingers crossed.
Once every four years I get to get my geek on and enjoy curling - you know that chess game played on ice, where curlers slip, slide, broom and push 44 pound hunks of granite (called stones) down a 125' sheet of ice into a ringed target called the 'house' while moving their stone around by causing the stone to curve and then stop their stone on a 2' wide circle in the middle of the house called the 'button'. Leave it to the Scots to invent a game using rocks and ice. (let's not forget they also invented golf - you know, putting a little ball into a tiny hole many yards away).
The ice used in curling is not smooth like the other ice-sports at the games but it is ultra-pure. The ice meister uses ultra-purified water generated from reverse osmosis technique to remove all impurities and any residual ionization (molecular charge) to make the crystal ice lattice as uniform as possible. Then after freezing the hard surface at -5degC (23degF) they sprinkle the surface with a mist of water to 'pebble' or texture the ice. The 44 pound stone then sits up on the pebbles and slides and curls more easily.
All the above requires that frozen water is slippery. So, the question still remains 'what makes ice slippery'? The reason athletes can gracefully slide on a frozen surface or we can slip and slide down our driveways is that every surface of ice has a molecularly thin watery layer on its surface. Its what creates this thin layer that is the real question. Until 2021, there were three hypotheses about the layer: (1) Pressure. When pressure is applied to the ice, a thin layer melts and creates slipperiness. (2) Friction. Whatever is sliding across the frozen surface (skates, skis, runners, stones) creates frictional heat which melts the top layer. (3) Premelting. This hypothesis states ice forms in a 3-dimensional lattice and ice exposed at a surface has broken away from this uniform lattice and behaves differently. At the surface ice molecules have fewer neighbors with which to bond and more freedom of movement - thus melting occurs along the surface.
In 2021, physicists at Complutense University in Madrid tested these hypotheses and developed a fourth. Amorphization was their conclusion. Here, they hypothesized the surface melting did not cause ice's slipperiness but rather the slipperiness is the result of non-uniformness within the ice lattice itself. For example, diamond cutters have long known it is easier to polish some sides of a diamond than others (the carbon lattice of the diamond isn't the same in all directions). Ice behaves the same way - ice is not the same throughout its entire 3d structure. They also discovered that sliding across the ice surface destroys the ice lattice order. It is these imparted irregularities or naturally occurring irregularities which creates ice's slipperiness. (Slip and Slide Here)
So no matter what ice you like - we can all have fun on its surface. But, stay safe regardless.
