What makes ice slippery

[Vet88 674]

Earlier there was a post that covered this but I can't find it so I thought I would post this in a new topic. For those that are interested in this type of thing, here is the latest study on the subject and what they found:

What makes ice slippery?

 

While the fact that the ice surface is slippery is widely acknowledged, it is far from being completely understood. Photo / File

 

 

 

 

 

 

 

 

 

 

Just in time for the first round of black ice crashes, scientists have explained what makes ice and snow so slippery - and it's a little more complicated than you might think.

And while the fact that the ice surface is slippery is widely acknowledged, it is far from being completely understood.

In 1886 Irish physicist John Joly offered the first scientific explanation for low friction on ice; when an object - such as an ice skate - touches the ice surface the local contact pressure is so high that the ice melts thereby creating a liquid water layer that lubricates the sliding.

The current consensus is that although liquid water at the ice surface does reduce sliding friction on ice, this liquid water is not melted by pressure but by frictional heat produced during sliding.

A team of German and Dutch researchers have now demonstrated that friction on ice is more complex than so far assumed.

Through macroscopic friction experiments at temperatures ranging from 0C to minus 100C, the researchers show that - surprisingly - the ice surface transforms from an extremely slippery surface at typical winter sports temperatures, to a surface with high friction at minus 100C.

To investigate further, the researchers performed spectroscopic measurements of the state of water molecules at the surface, and compared these with molecular dynamics (MD) simulations.

This combination of experiment and theory revealed that two types of water molecules exist at the ice surface: water molecules that are stuck to the underlying ice, or bound by three hydrogen bonds, and mobile water molecules bound by only two hydrogen bonds.

These mobile water molecules continuously rolled over the ice - like tiny spheres - powered by thermal vibrations.

As the temperature increased, the two species of surface molecules were interconverted: the number of mobile water molecules was increased at the expense of water molecules that are fixed to the ice surface.

Remarkably, this temperature driven change in the mobility of the topmost water molecules at the ice surface perfectly matched the temperature-dependence of the measured friction force, meaning the larger the mobility at the surface, the lower the friction, and vice versa.

The researchers therefore concluded that, rather than a thin layer of liquid water on the ice, the high mobility of the surface water molecules was responsible for the slipperiness of ice.

[beerleaguecaptain 999]

I never took physics...  this is why.  Its ice.  Its slippery.  Nuff said.

[YesLanges 127]

On 5/14/2018 at 4:12 AM, Vet88 said:

 

The current consensus is that although liquid water at the ice surface does reduce sliding friction on ice, this liquid water is not melted by pressure but by frictional heat produced during sliding.

The link doesn't open for me, but that part really seems counter-intuitive. First, wood and rubber floors (etc.) obviously have a much higher coefficient of friction against steel than ice, but I can't imaging that sliding a skate blade under pressure for a foot or two even on wood or rubber would produce enough heat to melt ice. Second, if it's friction, then you'd also expect that the surface of the blade would be a little warm to the touch after a long glide on the ice, which I highly doubt. Third, there's definitely much more friction between blade and ice sliding sideways while stopping than there is when a blade slides along the ice smoothly in a forward direction. So, if it's the friction of the blade against the ice, why wouldn't stopping on ice produce a slippery puddle in addition to shaving ice? 

[Vet88 674]

13 minutes ago, YesLanges said:

So, if it's the friction of the blade against the ice, why wouldn't stopping on ice produce a slippery puddle in addition to shaving ice? 

The stuff I have previously read on this said it was very small amounts of water getting produced by the heat hence no puddle. However that theory looks like it is now not the primary reason of slipperines with this theory of the mobile water molecules.

The article is here:

https://pubs.acs.org/action/doSearch?AllField=what+makes+ice+slippery&type=within&publication=344992248

but I don't have access. I will ask my daughter who is doing a chemical engineering degree to get me a copy.

[YesLanges 127]

Thanks...might as well ask her to weigh in, too. 

[Vet88 674]

Haha, she said it made her head ache even though she is a hockey player. Unfortunately she doesn't have full access either to the research paper (she is going to request it) but we can get some supporting information which gives a broad outline of their methods.

https://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.8b01188/suppl_file/jz8b01188_si_001.pdf

And if that gives you a headache, these guys here wrap it up quite well in an easy to understand sound bite:

https://www.zmescience.com/science/ice-slippery-h-bonds-8731058/