Walking is an act of moving in and out of equilibrium and we will learn more about walking in the unit on locomotion. In order to walk we:

1. Push against the ground with one foot using normal force and friction while leaning forward,  lifting the other foot, and moving it forward. This moves the center of gravity passes outside the support base formed by the (now) back foot. Having passed the tipping point, the body would fall except:
2. The front foot lands, slowing the forward motion of  your center of gravity and creating a new support base so that you are no longer past the tipping point. The front foot become the back foot and begins to pushes off.
3. Repeat.

Slipping happens when the friction coefficient between feet and walking surface is too small and the frictional force is not large enough to prevent your feet from sliding as the back foot pushes off and/or the front foot tries to slow the forward motion of your center of gravity.

Tripping happens when your foot does not move forward quickly enough to shift your support base below your center of gravity and you either fall over or have to rapidly move you feet into position just in time (stumble). Check you these AI simulations of creature that employ bipedal motion learning how to walk, and tripping along the way.

A YouTube element has been excluded from this version of the text. You can view it online here: https://openoregon.pressbooks.pub/bodyphysics/?p=1178

To see what AI algorithms can do when given a real physical body to experiment with, check out these robots.