Icy Windshield

Past week puzzle answer—any one of you folks up north going to test it?

So why did the can cause scratches, when the Mohs Hardness Scale says it should not have? Because aluminum is softer than glass, it should not have caused any scratches. But it did.

Here is the answer.

Apparently, something happens to aluminum when it is exposed to air.

The reason aluminum doesn’t rust is that shortly after it is exposed to the air, a coating of aluminum oxide is formed on any surfaces that are bare aluminum. And aluminum oxide has a hardness much greater than that of glass.

My brother didn’t agree with this one, by the way! He said that the thickness of the aluminum oxide would be too flimsy to scratch glass.

But we are gonna just go with it.

The puzzler answer is correct. Aluminum will scratch a windshield because of the oxide layer. Personal experience!

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This is what griding wheels are made out of! That and some bonding material to hold it all together.

I haven’t heard the podcast w/the solution yet, but my guess upon hearing the question was dirt on the surface was doing the grinding. Dirt contains some pretty hard substances. My bicycle’s aluminum cranks have been partly ground away, presumably by that method. Soft cotton pants leg rubbing on the dirt coated crank while pedaling.