Whether or not an ice cube will stick to your skin depends on the temperature of the ice cube and the moisture on the skin. The temperature of an ice cube can range from the freezing point of water 32° F (0° C) to well below this temperature depending on the temperature of the freezer and how long the ice cube has been out. It is important to note and often forgot that ice can get colder than 32° F. Typically you have a small degree of moisture on your skin that you aren’t even aware of. If the ice cube is very cold it will freeze the moisture on the skin and stick to you. If the ice cube is relatively warm, it will not stick. To release the ice from your skin, you only need to poor some warm water over the contact point.
This can be a surprising and fun phenomenon with everyday ice cubes from the freezer –because they don’t stick for very long. However, your tongue has much more moisture than your skin and therefore the ability to stick is even greater. Your tongue is also more sensitive which increases the OUCH factor of the experiment. Please do not stick your tongue to anything that is below a temperature of 32° F. In fact it’s probably a good idea to keep your tongue inside your mouth during most physics experiments.
Answered By: Kenneth S. Mendelson, Marquette University
For more information read: http://physicsbuzz.physicscentral.com/2009/12/tongue-in-cheek.html