Re: Why do droplets of moisture form on the outside of a glass with cold liquid

The cool liquid in the glass causes the glass itself to become cooler.  
When air comes in contact with the outside of the glass (especially if 
the air contains a lot of water vapor), the air may be cooled below the 
temperature where it can contain all the water vapor.  When that happens, 
some of the water vapor condenses into liquid water droplets on the 
surface of the glass.  In general, the colder the temperature, the less 
water vapor can be carried in the air.