Balance and Movement

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