It provides traction even on low friction surfaces. Both surfaces are smooth to allow the bearings to roll with little friction. Thus use of a lubricant reduces the overall system friction. Wheels have low bearing friction and pneumatic tyres give low rolling friction. Technique such as friction and vibration are used as well. Generally the force of rolling resistance is less than that associated with kinetic friction. Two sets are applied against the treads of the steel wheels for friction braking. The low, predictable friction of jewel surfaces reduces these variations. The science of friction and lubrication is called tribology. Air bearings are the chosen method for ensuring friction free travel. Glidants are used to promote powder flow by reducing interparticle friction and cohesion. Mechanical grippers can come in various types, including friction and encompassing jaws. This allows the steel to maintain its hardness in high temperature or high friction applications. It is also called rolling friction or rolling drag. Intertrigo is an inflamed skin condition caused by heat, friction, and moisture.