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This question already has an answer here:

I noticed that ice becomes stickier the colder it gets. I am reminded of the fool who stuck his tongue to a cold galvanized steel pole and got stuck to it. I am guessing that the pole was so cold that the moisture on his tongue instantly became ice. Why does ice have this property?

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marked as duplicate by Kyle Kanos, Carl Witthoft, Brandon Enright, John Rennie, JamalS Feb 15 '15 at 12:20

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ The reason for the "stickiness" of ice is the same as why your tongue would stick to a frozen pole, as given in the proposed duplicate. $\endgroup$ – Kyle Kanos Feb 14 '15 at 21:21
  • $\begingroup$ not really a dup, this is about ice, the other one is about a metal pole. $\endgroup$ – Shep Feb 14 '15 at 21:24
  • $\begingroup$ I think this question is confusing people: the title asks why ice is sticky; the text seems to meander between asking about the stickiness of either ice or cold metal (which obviously aren't the same thing); and the accepted answer explains why ice is slippery, which is a different thing entirely. I guess it's marked as a dupe now, but it would be nice to clarify what's being asked. $\endgroup$ – Shep Feb 15 '15 at 16:46
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It's really complex, and the answer from Shep is a bit imprecise.

Ice at temperatures just below freezing has the remarkable property of not being frozen on the surface. There is a extremely thin layer of liquid water on the surface. How thin? 70 nm at 272 K, but only 10 nm at 262 K. This water layer can act as a lubricant, but with less lubricant the friction is higher.

So, it's not the heat of your finger that causes the liquid layer. It's always there.

The second problem with Shep's answer is the idea of refreezing. It's unclear what he exactly means by that, but a heat wave is not like a wave in water. Heat will diffuse back. You don't get heat ripples.

The icy metal pole mentioned is quite effective in transferring away heat. Metals conduct quite well. The ice cube in comparison doesn't conduct well, and where molten the conductivity is even lower.

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  • $\begingroup$ Can't resist pointing out that you dang well do get heat ripples if there's a pulsed heat source. Or if you're applying heat to a superfluid. $\endgroup$ – Carl Witthoft Feb 15 '15 at 0:54
  • $\begingroup$ With respect to the refreezing, I just meant what you say; heat will defuse, it's not a wave. When you touch a really cold ice cube it sticks to your finger because the heat at the point of contact defuses into the cube. The effect is more pronounced in metal, because heat defuses faster there, but it will also work on ice. $\endgroup$ – Shep Feb 15 '15 at 5:54
  • $\begingroup$ actually, here's a good animation: youtube.com/watch?v=twBcpxrWm5E the cold parts start off by getting warmer, but eventually the small fluctuations reach equilibrium and the overall temperature drops (presumably because the outside is considered cold). $\endgroup$ – Shep Feb 15 '15 at 6:00
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It's only "sticky" when you stick it to something that was initially warmer than freezing.

Let's say you stick your finger against a (very cold) ice cube. Two things happen in sequence:

  1. The heat from your finger transfers into the ice and melts it slightly, forming a thin water layer.
  2. The heat dissipates further into the cube, and the water refreezes. When it refreezes it also freezes the surface of your finger. The ice crystals cross from the water into your skin pores, and form a lattice that includes some of your skin. This lattice makes your finger to "stick" to the ice cube.

Now if the cube is warmer, step 2 never happens, so the ice is never "sticky". In the case where you actually lick the ice cube (or metal pole), step 1 never needs to happen, the water that's there simply freezes.

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  • $\begingroup$ I think this misses the most important point, which is why ice (and snow) is slippery to begin with. To skate on ice you do not need to heat the blades of your skates; they will slide perfectly well even if the metal is below the freezing point. This is not something that is easy to explain. That the phenomenon should disappear at very low temperatures is easy to grasp by comparison. And a tongue sticking to a pole is quite unrelated; this is just that ice forms in the irregularities of the skin, forming a solid bond (not just friction!). $\endgroup$ – Marc van Leeuwen Feb 15 '15 at 10:45
  • $\begingroup$ Maybe the question "why is ice slippery" is more interesting to some people, that's not the question here. The question was about why ice sticky. $\endgroup$ – Shep Feb 15 '15 at 16:41
  • $\begingroup$ That may not be the principal question here, but without understanding why ice is not immediately sticky below freezing temperature, there is not much point in explaining why it becomes more sticky at much lower temperatures. But there is ambiguity in the question, I interpreted it as sticking to cold smooth surfaces like metal, not to your finger or your tongue, which may temporarily melt some of the ice. I see the question is closed now anyway, so maybe ignore my comment. $\endgroup$ – Marc van Leeuwen Feb 15 '15 at 16:52

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