Water; as ice (Introduction)

by David Turell , Saturday, December 16, 2023, 18:41 (133 days ago) @ David Turell

Expanded and floats:

https://bigthink.com/starts-with-a-bang/ice-skating-miracle-physics/?utm_campaign=swab&...

"...if you put thin blades on the bottoms of your shoes — ... As long as you can remain on your feet, with only your blades touching the ice, you’ll find that you can control your motion relatively easily, simply by applying forces through your feet (and the blades) to the ice down below. You can speed up, slow down, or change direction at will, and only if you fall or lose control of your skates (and body) will you wind up in a similar situation to the no ice skate case. It might seem miraculous, but there’s physics behind what you’re experiencing at each and every step. Here’s how it all works.

***

"Under different temperature and pressure conditions found on Earth and elsewhere in the Universe, different possibilities arise for how those various molecules bind together, creating a massive variety of possible configurations. At present, there are a whopping 20 known phases of ice, including:

"Ice Ih, which is normal hexagonal crystalline ice and the most common form of ice found on or near Earth’s surface,

"Ice Ic, which is a cubic crystalline variant of ice whose oxygen atoms are arranged in a diamond structure, that often appear at the lower temperatures found in the upper atmosphere,
And amorphous ice, which has no crystalline structure and is sometimes formed at ambient atmospheric pressure, in addition to the higher-pressure/temperature phases of ice: Ice 2 through Ice 18.

"However, it’s the most common form of ice, plain old Ice Ih, that’s relevant for the problem of ice skating. Normally, under this configuration, the water molecules within ice are arranged in a hexagonal crystal lattice, and adding new water molecules to these icy structures will simply result in the growth of the main crystal in the same ongoing pattern. Adding more molecules won’t change the structure of your ice,

***

"...the most common fate of hexagonal crystalline ice — the type of ice found on Earth’s surface — is that either heating it or compressing it will simply cause it to melt.

***

"This is incredibly important, and forms the physical basis for how ice skating can physically occur. If water/ice behaved like most materials, then simply by applying greater and greater amounts of pressure to the liquid phase would force it into a solid phase, as the atoms/molecules inside would achieve a more tightly-packed configuration.

"But water is different than most materials, in that when you freeze it, it actually expands from a liquid phase into a solid phase, occupying more volume as a solid than it did as a liquid. And this means, even if you apply a tremendous amount of pressure to liquid water, it remains liquid. But if you apply that same amount of pressure to solid water (ice), it can transition into a liquid phase.

***

"That’s where the idea of ice skates becomes so powerful. Instead of distributing the force from your body, which can approach nearly 1000 Newtons for an average human being, over a substantial area (your footprint), they instead decrease your area tremendously: down to a long, thin “blade” of metal. If a typical skate blade is 30 centimeters long (about 1 foot) but only about 1 millimeter thick, that can create a pressure of up to three million pascals (a Newton-per-square meter) for a typical human who puts their weight down on one ice skate: about 30 times the normal amount of atmospheric pressure!

***

"First, the top layer of ice, the one in contact with their skates, turns to liquid just as their skate glides over it.

"The fact that there’s a thin, lubricating layer of liquid water between the skate above it and the solid ice beneath it reduces the skater’s friction even further.

"The liquid water, as we discussed earlier, fills in the small imperfections in the ice, creating an even smoother, lower-friction interface.

"Because there’s a decrease in the ice’s volume when it melts into the liquid phase, this creates a small “groove” in the ice for the skater to travel in.

"And finally, when the skate finishes passing over the portion of the ice that was melted, the sudden “drop” in pressure immediately causes the melted water to re-freeze, becoming ice once again.

"In other words, even though we call it ice skating, the reason it’s so successful is because the skater is actually skating atop a thin layer of liquid water!

***

"If water and ice were more like the typical materials found throughout the Universe, where their solid phase is denser and has their component particles more tightly packed than their liquid phase, then ice skates would never work. Increasing the pressure over a thin region of surface would simply compress the solid, rather than melting it into a liquid phase. That’s the key property — rarely found in nature, but belonging to water and only a few other chemical compounds — that enables the high-pressures exerted by all of a human’s weight being focused down onto a narrow blade to melt, and glide over, the ice."

Comment: water's strange characteristics make it vital for life. Note that hydrogen and oxygen were some of the earliest formed elements. That is how a designer would work, set up important items early on in preparation for the future.