Load Carrying and Slip Length

Slipping and falling is a major economic problem. Past research has concentrated on the relationship between the shoe and the floor surface while more recent research has extended into the human factors of slipping. The measurement of slipperiness, as opposed to the coefficient of friction, depends on a thorough understanding of why slips start and how the human ends or avoids them. Strandberg identified the ratio of the horizontal force to the vertical force in determining the limiting point in slip prevention. One implication would be that if the vertical force were increased, for example, by load carrying then the tendency to slip would be decreased. This appears counter intuitive and an experiment was performed to investigate it. Five subjects were exposed to a slippery surface while protected from falling. Three conditions were evaluated; no-load, back mounted load, and front mounted load which were designed to minimize any gait changes. The addition of the load significantly increased the average slip distance at both slow and high speeds, although the differences between a front and rear loading did not reach significance. This suggests that it is not sufficient to identify the maximum frictional demand, but account should be taken of the frictional availability at various parts in the heel strike slip stop cycle. Thus methods of measuring slipperiness to determine potential slip and fall accidents must accommodate measurements over the whole cycle and must allow matching with the friction demands of Strandberg.