McGill Alert / Alerte de McGill

Updated: Thu, 07/18/2024 - 18:12

Gradual reopening continues on downtown campus. See Campus Public Safety website for details.

La réouverture graduelle du campus du centre-ville se poursuit. Complément d'information : Direction de la protection et de la prévention.

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Is there a difference between real snow and "artificial snow"?

Yes, there is. "Artificial snow" isn't really snow.

Snow-making machines actually make tiny beads of ice, each one about one ten-thousandth of an inch in diameter. Water is sprayed from a hose together with compressed air. The air is needed because as it quickly expands, its temperature drops since it has to do work by pushing away air molecules. This cooling helps freeze the water. As the water freezes, it releases heat. This should be obvious when we realize that in order to melt ice, we have to add heat. The heat released is then taken up by the expanding compressed air. This is why the "snow-making" pipes are always high in the air. If the snow were made close to the ground, the heat released by the freezing process would actually warm up the ground and melt some of the snow.   

The same principle is used by farmers who spray their crops with water when a freeze is in the forecast. It is a common misconception that the thin layer of ice produced acts as insulation. Not so. The freezing water liberates enough heat to keep the water inside the fruit from freezing. And why does skiing on artificial snow feel different? When skiing, pressure causes the snow to melt, increasing slipperiness. But the contact surface is not the same for real snowflakes and artificial ice beads and their temperature can also be different.  So, the rate at which they melt under pressure can be different.  Expert skiers will notice a difference, but those with meagre talents will only notice that it hurts more to fall on the artificial stuff.


@JoeSchwarcz

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