Why do Glasses sweat?
When the water vapor that is present in the atmosphere touches any particle in the air, it condenses into liquid droplets. This will fall in the form of rain. Condensation is a process where there is decrease in temperature of the gas or air. The warm air will have high energy and moves faster and spreads wider. The cool air consists of molecules which come closer and slow down their movement. This process of reducing the movement of molecules and coming closer to each other is called condensation.
Similarly, the glass with cool liquid inside it or any drink added with ice cubes inside the glass makes the walls of the glass cooler. The water vapor that surrounds the glass is warmer than that of the liquid inside it. So the surrounding air keeps the glass warm while the cold temperature of the liquid inside it makes the vapor on the warm glass to condense. These condensed forms of vapors appear as droplets on the glass. These drops are seen as sweating on the glass.
It can be said in another way too. The air consists of water vapor. The percentage of water vapor might differ depending on the warmness in the weather. Even in the desert also little water vapor will exist in the atmosphere. When this vapor touches the glass containing cold liquid, it loses its energy and becomes liquid. The vapor condenses on the solid glass wall to turn into liquid droplets. These drops appear as if the glass is sweating.
Even the sunglasses that we wear on our eyes also fog up when we move from the air-conditioned room into the hot weather outside. This happens as the hot air containing the water vapor immediately condenses on the cool sunglasses resulting in the formation of very small liquid drops. These drops cover the glasses as fog.