# Ice skating, how does it really work?

Okay, some textbooks I came across, and a homework assignment I had to do several years ago, suggested that the reason we can skate on ice is the peculiar $p(T)$-curve of the ice-water boundary. The reasoning is that due to the high pressure the skates put on the ice, it will melt at temperaturs below $273 K$ and thus provide a thin film of liquid on which we can skate. It was then mentioned as fun fact that you could ice-skate on a planet with lakes of frozen dioxide because that gas has the $p(T)$-curve the other way round.

My calculations at that time told me that this was, pardon my french, bollocks. The pressure wasn't nearly high enough to lower the melting point to even something like $-0.5$ degrees Celsius.

I suppose it is some other mechanism, probably related to the crystal structure of ice, but I'd really appreciate if someone more knowledgeable could tell something about it.

• I'm pretty sure this was a problem on the final exam for my undergrad thermodynamics class ;-) so at least I think your calculation is reasonable. I don't know/remember what the real reason is though. – David Z Dec 7 '10 at 5:31
• Well, this analysis completely ignores that when you skate you are not standing but you are actually moving. There should be some friction between the skates and ice and this should provide enough heat to melt the ice and create a thin water film. At least this is my intuition (perhaps completely wrong). – Marek Dec 7 '10 at 11:44
• The binding energy near a surface is different than the binding energy in bulk, and it is possible that you melt a thin surface layer without melting the bulk. – Ron Maimon Aug 21 '11 at 14:14
• A new publication on the issue: phys.org/news/2018-05-slipperiness-ice.html – asmaier Sep 6 '18 at 12:06

Yup, this is true that the pressure is too small, but the true explanation is not justified yet. Nevertheless the common sense is that there is a lubricating film of water or at least anomalous ice. For an overview, see: http://lptms.u-psud.fr/membres/trizac/Ens/L3FIP/Ice.pdf

• The pressure is too small for bulk melting, but surface melting is different, and this is the relevant issue. Compressing a surface of water-ice will melt some surface, but compressing the surface of other materials will solidify any surface liquid, because liquid ice has a smaller volume. The explanation is fundamentally correct, the bulk melting is irrelevant. – Ron Maimon Sep 23 '11 at 17:10
• @RonMaimon: If there are any irregularities in the ice, or the blade, wouldn't the pressure at those points be nearly infinite unless or until the H2O underneath them gave way? I would think at least some of the weight of the skater would be borne by liquid water unless the compressed water liquified, reshaped itself to a lower-pressure configuration, and refroze. Would skis be effective at -35 on a polished frozen sheet of ice? – supercat Nov 29 '14 at 16:14
• @supercat: The pressure won't be infinite because Young modulus of ice is not infinite - it is not infinitely rigid; it's compressible to a degree and will yield (compress) under pressure a little. It may also locally break destructively and get displaced as dust/shards without phase change. – SF. May 17 '18 at 22:59
• @SF.: I would regard compression, breaking, and melting as forms of "giving way". My point is that even if there wouldn't be enough pressure for ice to melt if weight were uniformly applied on a skate, some areas under a skate will usually be under much higher pressure than others. – supercat May 17 '18 at 23:11

The assertion that the skate does not exert enough pressure to melt ice is wrong. Imagine that the skate is lowered vertically until it touches a perfectly flat surface of ice. The initial contact area (before the blade starts to sink into the ice) would be incalculably small and the initial pressure incalculably large because of curvatures. A typical freestyle blade’s “rocker” has a radius of 6 feet; its “hollow” of 7/16 to 10/16 inch. The blade is typically 0.15 inch thick, so its two edges have “bite” angles of 7 to 10 degrees. The rate at which an edge could melt ice and sink in would be limited by heat conduction. In a dynamic situation, with the skater gliding along at a good speed, viscous dissipation in the thin layer of lubricating water would generate some of the heat. If the skater’s trajectory is curved but the rocker’s curvature multiplied by sin(tilt) is poorly matched to the curvature of the trajectory, then there will be additional friction and sound effects as the edge chews up the ice.

Well, having a solid block of ice. Atatch weights to a string on both ends and hang it over the ice. The string will go trough the ice over a period of time, without actually cutting the entire block. How does this happen? possibly the pressure melting minescule ammounts of ice underneath the string and the water refreezing above the string.

I remember reading in a book (on surface physics) during my grad study on this topic. There was a diagram on friction of a steel "skate" on solid argon at and below argon melting temperature. The diagram was qualitatively identical to the same experiment for ice. Friction dropped to low values when temperature aproached melting point. Argon melts regularly, for that reason pressure melting is not possible. I regret that I did not memorize the title and author of that book :=( Georg

Another fact against 2pressure melting": how does skiing work? The pressure under a ski is very low.

• That doesn't argue against pressure melting at all. Why would you expect skiing and skating to exploit the same mechanism? Why would you expect snow and solid ice to have the same properties? – David Richerby Feb 12 '14 at 14:41

Regelation-Regelation is the phenomenon of melting under pressure and freezing again when the pressure is reduced. Many sources state that regelation can be demonstrated by looping a fine wire around a block of ice, with a heavy weight attached to it.

Ice skaters shoes :

Whole weight of skater is concentrated at this small portion of area,thus ice under shoes melts quickly [due to Regelation] converting ice to water (notice that due to high pressure ice converts to water without increase of temperature , generally ice melts at 0℃). Hence due to replacing of some amount of ice with water, friction of surface decrease and skater moves easily.

Why to use term regelation? Since due to pressure (or) strain , small amount of ice is coverted to water,whole ice does not break(,melt),making skating possible.

Also: people tried to add on wiki,edit summary

• The part on ice skating was added to the wikipedia entry as a misconception. Unless you can prove otherwise I think it is unwise to cite that wikipedia entry as a source. – JMac Mar 10 '17 at 14:13
• @JMac yes,but if you see edit history (to which I have provided link) people tried to add it as a reason. At last who knows it will change in few days or months or years? – Fawad Mar 10 '17 at 14:15
• It was removed 10 years ago and still not added back. It was also cited with a source in the misconceptions (I don't currently have access to the source). Unless you can provide some good proof of this, you are going against the other things said and the purpose of this thread. The point being that the burden is on you to prove this pressure is enough for the stated effects. Many sources don't believe it is a good enough explanation. – JMac Mar 10 '17 at 14:21
• @JMac c'mon , regelation is called when when we apply pressure on ice and that turns into water. But when that pressure is removed,water again coverts into ice. Don't you this this is what happens while skating? – Fawad Mar 10 '17 at 14:35
• The pressures from skates don't seem to be nearly high enough to temporarily melt ice at temperatures even like -1° C. The issue isn't that regulation isn't a thing. The issue is that quantitative analysis of the situation shows that the effect isn't great enough to even cause localized melting. You would need pressures you wont achieve by skating on ice, so additional factors are required to describe the phenomenon. Your answer provides nothing beyond what the OP already described, and then described his issue with it. Unless you can mathematically prove otherwise, this doesn't answer it – JMac Mar 10 '17 at 15:05

It was shown that surface water molecules vibrate more strongly than those in the bulk, having less neighbor molecules to interact with. Apparently, this creates a nanometric film of quasi-liquid water that reduces friction.

• this is only true up to certain temperature below which you need not have a layer of water. – mythealias Nov 10 '12 at 18:41