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Date: Around 1993


Question:
Why is it easier to maintain your balance while gliding on one ice-skate then while standing still on one ice-skate?



Replies:
This is essentially the same as the reason why it is a lot easier to keep your balance on a moving bicycle than on a stationary one. The point of contact with the ground in both cases is well below the center of mass. That means that, when moving, there is a net angular momentum about that "pivot" point. If you are slightly off balance, your center of mass is not directly over the pivot point, but to one side of it. Then the force of gravity starts pulling you down, but because of the angular momentum (just like with a gyroscope) this gets changed into a turning motion - you change direction a little by leaning to one side or the other, and if you keep leaning in the same direction you will go around in circles. Of course there is some point (you lean too far, or slow down too much) where gravity wins out and you just fall over. But the faster you are going, the more stable you will be.

A. Smith



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