Squeaking skates

Did you know that skates squeak when it’s cold enough?

I think the squeaking may be related to surface melting. This unsolved physics problem has been attracting a lot of interest because it affects many materials, not just ice. Robert Rosenberg summarizes it in his 2005 article “Why is Ice Slippery?“.

The most common explanation of how skating work is the “pressure-melting” hypothesis: skating is possible because skates melt a thin layer of water on top of the ice to glide on. There are some problems with this explanation. For one thing, if pressure-melting is really behind how skating works, it should stop working at about -3.5 degrees Celsius (25.7 degrees Fahrenheit). It doesn’t (Rosenberg, 50).

In fact, there’s always a thin layer of liquid (or liquid-like) water on top of ice. Michael Faraday figured this out in 1859 when he noticed that when you hold two ice cubes together, they freeze into one. Rosenberg describes a more recent experiment in which researchers measured the force required to pull two ice spheres apart. The colder it got, the less force was required, which means the film gets thicker as the temperature gets higher.

It’s possible that the recent low temperatures thinned the film on the surface of the ice enough to make my skates squeak. When a door squeaks, you put oil in the hinges to lubricate them. Perhaps there wasn’t enough oil (in the form of a liquid-like layer) to keep my skates from squeaking like there usually is.

I’ve observed other skates squeaking at higher temperatures. The layer thickness needed probably depends on several factors: how sharp the blades are, how they’re shaped (including the radius of hollow and the rocker), and the weight of the skater.

References

Michael Faraday. 1859. “Note on regelation.” Proceedings of the Royal Society of London 10:440–450.

Robert Rosenberg. 2005. “Why is ice slippery?” Physics Today 58.12:50–55.