MadSci Network: Physics

Re: What is the scientific reason that people slip while walking on wet or icy

Date: Mon Oct 19 12:44:58 1998
Posted By: John Link, MadSci Admin
Area of science: Physics
ID: 907766646.Ph

The question is, basically, why is a sidewalk (for instance) slippery with water or ice on it?

The reasons are two.

First, friction is less between the bottom of the shoe and the sidewalk with a layer of water than it would be between the shoe and a dry sidewalk.

Second, ice is an interesting substance which has a raised freezing temperature under increased pressure, so when you walk on the ice and the pressure on the ice is increased a thin layer of ice melts and becomes liquid water, so, again, the friction is reduced. When you are on ice the friction is even less than on just a wet sidewalk because the still-frozen surface of the ice is very smooth.

You can find more information about this by looking at books that describe the "triple point" of water or the characteristics of ice, and also books that discuss friction. Try looking at some of the sources available at the MadSci network, but don't stop there!

John Link
MadSci Scientist and Administrator

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