Why do glasses fog up?
Show answer & explanation
Answer: Water vapor condenses on cool lens
Water vapor condenses on cool lens ✓ — Correct! Warm air holds more moisture (water vapor) than cool air. Warm breath meets cold glasses—air cools rapidly, can't hold as much moisture. Water vapor condenses into tiny liquid droplets on lens—fog! Dewpoint: temperature where air becomes saturated. Same principle: bathroom mirrors after shower, car windows in winter. Anti-fog coatings reduce surface tension, preventing droplet formation!
Temperature creates tiny clouds — Wrong. Temperature difference drives process, but specific mechanism is condensation—water vapor becoming liquid droplets on cool surface.
Breath contains particles — Wrong. Breath has moisture (water vapor), but fogging occurs when vapor condenses to liquid on cool surface, not particle deposition.
More Physics in Daily Life questions
- In a warm office that already reads 26 C, which change can make people feel cooler without lowering the thermostat?
- Why might 26 C feel acceptable in a breezy naturally ventilated summer building but too warm in a sealed winter office?
- On a warm, humid day, why can a 27 °C room feel worse once your skin is sweaty?
- Why can moving air make a 27 C room feel cooler without changing the thermometer?
- Why can a desk beside a cold window feel chilly even when the thermostat across the room still reads 22 C?
- Why might someone who just climbed stairs feel warm in a 22 C room while someone sitting in a T-shirt feels chilly?