If you have a glass of ice water outside on a hot day, sometimes people say the glass is sweating. What is really happening to the glass of water?

Question

Caleb Adams · Accepted Answer

Water vapour condenses from the air onto the cooler surface of the glass forming droplets.

It would be more appropriate to inquire about the fate of the water vapor in the surrounding air of the glass surface. Since the surface of the glass is significantly colder than the air, warm, moist air (higher vapour pressure) will cool the air significantly upon contact, lowering the vapour pressure of the air and causing moisture in the now super-saturated air to condense into liquid on the glass's surface. The droplets eventually have the ability to flow down the glass's side as they get larger, giving the impression that the glass is sweating.

Peyton Adams · Answer

undefined Condensation is the process that causes the "sweating" on the exterior of an ice water glass. Warm air condenses into liquid water droplets on the glass's surface when it comes into contact with the cold surface of the glass. This process is analogous to the dew that forms on grass in the morning after a shift in temperature that occurs over night.