The effect of normal load, speed and moisture on footwear traction

Abstract

Background: Numerous studies have tested footwear traction using various normal loads and movement speeds, and on different surfaces. However, because of the divergence from Amontons’ laws of friction, the results of studies that tested footwear traction using different normal loads or movement speeds are difficult to compare. The purpose of this study was to investigate how alterations of normal load, speed of testing and surface moisture affect footwear traction. Method: Data were collected on three types of footwear using a portable traction tester on the field of play of a natural grass and an artificial turf football field. Testing was conducted with different normal loads (335, 433, 580, 678 and 776 N), movement speeds (50, 100, 150 and 200 mm s−1, and 30, 60, 90° s−1) and amounts of moisture added to the field to determine the effect each variable had on traction. Results: Surface moisture had a large effect on traction and was shoe and surface specific. Normal load had a linear effect on traction with the ranking of the footwear staying consistent, indicating that testing at small normal loads may be sufficient. Movement speed had a linear relationship for translational traction but was constant for rotational traction, with the ranking of the footwear staying consistent again, indicating that slow speeds may be sufficient for testing. Conclusions: The relationships found are only valid for the method of testing used in this study, and for the range of loads and speeds tested. The relationship may fail to remain linear at higher or lower loads or speeds. Future studies should continue to examine the effect that moisture has on footwear traction to better understand how shoes react to changing conditions.