[Physics] Why does motion help you balance on ice skates

Question

It's almost impossible to balance on a single ice skate if you're standing still. But give yourself just a little forward motion—it doesn't take very much—and it suddenly becomes easy. You can stand there on one leg and glide effortlessly half way across the rink. Friction will cause you to gradually slow down, and it's only when you've slowed almost to a complete stop that balancing becomes hard again. Why?

This seems suspiciously similar to the question of why it's easier to balance on a moving bicycle. But the standard answer to that involves the angular momentum of the wheels. There's nothing rotating here. In fact, other than the very slight deceleration from friction, moving should make no difference. In both cases, you're standing still in a nearly inertial reference frame.

Does that slight deceleration somehow matter? Or does the interaction between the ice and a moving skate somehow help you to balance?

Answer 1

I assume you are talking about skates for figure skating (and not about skates for speed skating).

Figure skates are not straight. Along the length of the foot there is a curve, in the vertical plane.

As you are gliding over the ice your sense of balance feels it when your center of mass is no longer precisely above your contact point. You correct by pointing the skate ever so slightly in the right direction to move your point of contact back underneath your center of mass. Pointing ever so slightly is enough; the motion of the gliding does the rest

It may even be that you don't need to make that adjustment actively. When the shoe with the skate leans to the right I assume the skate itself will tend to follow a slight curve to the right, automatically bringing your point of contact back underneath your center of mass.

(I have some limited experience with speed skates, that's why I'm offering guesses rather than speaking from direct experience.)