# Why do ice cubes stick together or to the edges of a drinking glass?

I was drinking iced-water from a drinking glass (made of glass) at a restaurant yesterday when I was taking a drink, I noticed that there is very little ice water coming out and then suddenly, the ice water mixture comes crashing down. With my open mouth overfilled with ice water, my shirt gets wet – I hate when this happens. After drying myself off, I started thinking why this does happen:

1. How does ice that starts off loose and separated in water fuse together to form one large clump?

2. What causes the ice-water mixture to stop flowing momentarily and then suddenly starting flowing again? Is it that the ice fuses together in the glass and forms one large clump, and then the friction with the edges builds a "dam-like" situation? Or are there individual pieces of ice fusing with the edges of the drinking glass damming-up the ice?

• What do you mean by "ice water"? I fail to understand the whole question because of this phrase. Aug 11, 2013 at 14:26
• I mean a glass of water that has ice - an ice-water mixture. Aug 11, 2013 at 14:52
• @John Rennie that is not what Carlos asked Aug 11, 2013 at 15:53

Once again, being at a restaurant with friends, I go to drink iced-water from a drinking glass again, and sure enough, this very thing happened again. Perturbed and determined to figure why ice fuses together like this, the experimentalists came out in me and I started pouring water into glasses full of ice when I got home. I believe that I have an answer to my own question.

Even though an ice water mixture maybe at 0℃, the temperature of the ice depends on how long the ice has been in the glass of water. If the ice has been in the water for some time, then the ice eventually will reach it maximum temperature of 0℃. However, ice fresh out the ice freezer, will be colder (FDA recommends -20℃) in the inside than the outside and this holds the key to why ice will fuse together in a glass of water.

Fresh Ice at -20℃

Starting off with ice at -20℃ and pouring water into the drinking glass, the edges of the ice and water will be in thermal equilibrium at 0℃ after a short period of time. However, in order to freeze the water in-between the ice cubes, latent heat must be removed in order to freeze this very water. (Remember that latent heat of fusion is the required amount of heat that must be removed to change water into ice.) This is an image I created to show you what I am thinking here.

The dark blue regions indicate the colder -20℃ internal regions of the ice cubes whereas the light blue regions indicate the warmer 0℃ regions of the water as well as the edges of the ice cubes. The red arrows indicate the directions of the latent heat of fusion being removed from the water, and therefore, freezing the water in-between the ice cubes. I also see no reason why ice will not fuse to the sides of the glasses as well, using this same mechanism to remove the required latent heat. To test this, I poured water into glasses filled with fresh ice into several drinking glasses filled with water and was able to get the ice to fuse.

“Old Ice at 0℃”

Starting with fresh ice again, I now constantly stirred the ice around so that I did not allow them to fuse together, and after about 10 minutes or so, I let the ice sit in the glass undisturbed. I found that the ice never fused together. This makes sense because I think that the ice is now at 0℃ throughout the whole ice cube. As a result, there is no way to remove the required latent heat to freeze the water in-between the ice cubes or the sides of the drinking glass.

1. OK as much I think when two ice cube come together and their sides stick to each other the water on the surface between the two cube starts freezing because on both the sides there is only ice which brings down the temperature of the water between the cube to freezing point which causing the water between then to freeze and the two cubes to join together forming a lump. This property of ice is used in many fields like in ice sculptures making competition in which players use water to join two ice slabs or any other part

2. I can't say much about your second question but as much I think the ice cubes stick to the glass wall for a moment and when you again hold the glass the connection between the wall of the glass and the ice cube gets weaker due to the heat of your hand and the cubes then slips and jumps onto your T-Shirt, but I don't know much about it so wait other answers will help me too

• With regard to point 2, I suggest it is more likely that the act of raising and tilting the glass simply causes the (relatively) warm water to circulate faster which causes the weak layer of ice between the cube and the glass walls to melt. This of course depends on how you hold the glass, I would hold a glass loosely, with the tips of my fingers and thumbs making contact, whereas I imagine some would grab the entire thing in their fist. Aug 11, 2013 at 15:25
• yes, you are right but don't you think that it will take much longer time to melt the ice in the Central part whereas the heat from the palm may do it a little bit faster Aug 11, 2013 at 15:28
• @Akash: can I not assume that the ice-water mixture is in thermal equilibrium? If this is true, then your argument about the temperature between two ice cubes doesn’t hold. If it is not true, why is the ice’s temperature greater than $0^oC$? Aug 11, 2013 at 15:58
• @Akash and Mark: I thought that glass was a relatively poor thermal conductor; furthermore, my fingers holding the glass have limited area contact and transfer very little heat. Is this small amount of heat transferred enough to dislodge ice stuck to the edge of the glass (assuming it is the ice pieces sticking to the glass)? Aug 11, 2013 at 15:59
• @Carlos Ice and water are not in thermal equilibrium. Thermal equilibrium mean's that the two bodies are at the same temperature and you know that ice and water can not be liquid and solid at same temperature hope get what i am trying to say the ice is below $0oC$ and water is above that. And yes glass is a bad conductor but it not a insulator so since the glass wall's are too thin to stop the heat it flow's through it Aug 11, 2013 at 16:05