Today I watched a glass of ice water "sweat" on the kitchen counter and reminded myself that condensation isn't the water leaking through the glass. It's water vapor from the air turning liquid on the cold surface. I used to think humid air was "heavier" because it felt thick, but water vapor is actually lighter than dry air—individual H₂O molecules weigh less than N₂ or O₂. The confusion comes from the fact that humid air often coincides with low-pressure systems and still conditions, which make the air feel dense.

I ran a tiny experiment: I filled two identical glasses with ice water, then wrapped one in a dry towel. After twenty minutes the bare glass was dripping, the wrapped one bone-dry. The towel insulated the surface, keeping it above the dew point. It's a reminder that condensation needs a cool surface and available vapor. Change one variable and the outcome flips.

A neighbor asked why her car windows fog up in winter. I explained that warm, moist breath hits cold glass, and boom—instant fog. She said, "So I'm basically making clouds inside my car?" Close enough. I didn't correct her because the analogy works: both processes involve vapor condensing on nucleation sites, whether dust particles aloft or a chilled windshield.

One limit I should mention: dew point calculations assume well-mixed air. In a small, enclosed space like a parked car, local humidity and temperature can vary by a lot, so the simple formula breaks down. I've seen people obsess over precise dew-point numbers when the real answer is "crack a window."

The practical takeaway? If you want to stop condensation, either warm the surface above the dew point or reduce the humidity. That's why dehumidifiers work in basements and why double-pane windows beat single-pane. Physics doesn't care about your aesthetic preferences—it just follows temperature gradients and vapor pressure.

Later I found a tiny puddle under the glass and realized I'd been so focused on explaining condensation that I forgot to use a coaster. Small mistake, easy fix. Sometimes the best lesson is the one that leaves a water ring on your table.

#science #condensation #humidity #learning #physics