When the temperature is very cold I often hear people say that the pavements are "like glass" meaning that they are very slippery. Does glass and rubber (soles of shoes) make for a slippery situation when it comes to walking? I would have though rubber on glass produces a fair amount of friction.

Perhaps the reference (which I don't think I've ever heard, at least in my culture) is because glass isn't a very porous material, and is very slippery when it's wet. Surely the saying refers to icy conditions and not just cold ones? Rain that freezes on the pavement can seem like wet glass.

During very cold weather conditions when the pavements become covered in ice and snow the saying "it's like walking on glass" refers to the fact that the surface one is walking on is very slippery. On a similar note one also hears the saying (here in the UK at least) "The roads are like glass" again this refers to them being very slippery due to the icy conditions.

I've never heard that expression. Rubber has plenty of friction with glass, though. Or dry glass, at least. Why not get a window wet and try rubbing a sneaker on it?

That's what I was thinking. I was checking whether the saying had any scientific validity but clearly it doesn't.

 

Below is a quote from a newspaper (The Press) from the UK which illustrates the saying nicely.

 

"And Tim Stockdale, of Osbaldwick, said: “The roads are like glass and the paths are absolutely impossible to walk on – it’s a complete nightmare. It’s like an ice rink – it’s completely out of control and I feel very sorry for any elderly people.”

Well, +1 for Americans vs. British in category: accurate representations of friction in cliched similes.

 

USA! USA!

Ice is generally transparent, colourless, smooth, cold to the touch, and slippery when it's wet; so it's nothing like glass at all.

Anyone who has ever dropped a glass while washing it or because its surface was wet will know that wet glass is quite slippery. Aparently newspaper editors in the UK can cope with this and so can the readers.