It's a cold day outside. When you come inside your warm house, the glasses that you're wearing get moisture on them and it's hard for you to see through them. You say to your sister, who's sitting in the house:
My glasses are fogging up.
When a piece of glass gets moisture on it, you say that it's "fogging up". Some things that often "fog up" in day-to-day life include:
- bathroom mirrors
- people's glasses
- the windshield of your car
"Fog" is a kind of cloud that appears close to the ground and makes it hard to see things. When fog appears, you can say that "it's getting foggy". But you only say "it's fogging up" for objects that you can see through.
There's also a scientific word for the water that appears on something when the air changes temperature. It's called "condensation". So to explain something "fogging up" in a scientific way, you can say:
When a cool object is exposed to humid air, water vapor in the air turns to liquid water, and condensation accumulates on the object.
- the "glasses" that people wear to help them see are always plural.
- "a glass" is something you drink out of. More than one of them is called "glasses".
- "glass" is a type of material. If you want to count individual sheets or broken pieces of it, you say "a piece of glass" or "pieces of glass".
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