We are experiencing warmer weather than normal, which is causing the snow to melt and re-freeze daily. This has led to very slippery conditions.

A few years ago, I was running in similar conditions, and I got to an area where the ice started to feel more slippery. So my reaction was to stop running and start walking. To my surprise, it was harder to walk in the icy conditions than it was to run: it felt as I was slipping with every single step.

Today, in light of the conditions, I tried the experiment again, and my sensations seemed to confirm what I felt the previous time.

Is there any physical basis to what I felt? Is it possible that running on ice produces a more stable footing than walking does?

If it makes any difference, the ice is of course not smooth, and one is usually slipping on the "slopes" of small creases.



"Biomechanics researchers Timothy Higham of Clemson University and Andrew Clark of the College of Charleston conclude that moving quickly in a forward, firm-footed stance across a slippery surface is less likely to lead to a fall than if you move slowly. Approaching a slippery surface slowly hinders the necessary task of shifting the center of mass forward once foot contact is made."

"The key to avoiding slips seems to be speed and keeping the body mass forward, slightly ahead of the ankles after the foot contacts the ground."

"Once the knee passes the ankle during contact with slippery ground, slipping stops."

  • $\begingroup$ Agreed. Faster digs in better, breaks thin ice, and gets you there quicker than slow walking. It's also the technique used for boom running. Arguably running like crazy has an element of efficiency, but there's a much greater incidence of falling; which if you spend your time licking your wounds instead of getting back on your horse the time saved is wasted. $\endgroup$ – Rob Feb 11 at 16:39

There would seem to be two opposing factors:

  1. To avoid the ratio of (a) the transverse force between your shoe and the ice to (b) the force that your shoe applies normal to the ice must be less than the coefficient of static friction, $\mu_s$:

    $$ \frac{F_\text{transverse}}{F_\text{normal}} <\mu_s $$

    This probably favors walking over running but this may depend on your running or walking style.

  2. As the ice melts, the surface becomes much more slippery. More ice will melt the longer that your (warm) shoe remains in contact with the ice. Since running likely involves faster foot steps, this favors running over walking.

In sum, which is better depends on your running vs walking style and on the temperature difference between shoe and ice.


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