At the same time the trailing foot remains in contact with the walkway, continuing to bear part of the load until the forward heel rocks forward, gradually accepting the full load as the entire foot contacts the walking surface. During the walking process, the upper body's center of gravity moves forward at a fairly constant rate, its support being continuously shifted from leg to leg. Walking can be thought of as the process of repeatedly losing and gaining body support by one leg and then the other, with one leg taking over support of the upper body as the other leg begins to lose support. Balance of the upper body during walking activity is also a dynamic process. Not only is balance of the whole body being shifted from leg to leg while walking, such balance must be continuously adjusted on the stationary leg during the time of opposite leg swing.
Coefficient of friction is used as a measure of slipperiness.
Coefficient of friction is the ratio of the force required to move one surface over another, overcoming friction, divided by the vertical or normal force pressing the surfaces together. The horizontal component of the force exerted by the forward leg on a level walking surface during the normal walking process reaches a maximum in the forward direction shortly after the heel makes contact with the walkway. This horizontal component is the force that must be counteracted by the friction characteristics of the walking surface in order to avoid slipping. The generally accepted COF standard today relative to slipperiness is that a static coefficient of friction of 0.50 or above is relatively safe on a dry surface. A COF reading below 0.50 indicates an unsafe surface in terms of friction.