Traction (engineering)

Traction, or tractive force, is the force used to generate motion between a body and a tangential surface, through the use of dry friction, though the use of shear force of the surface is also commonly used. Traction can also refer to the maximum tractive force between a body and a surface, as limited by available friction; when this is the case, traction is often expressed as the ratio of the maximum tractive force to the normal force and is termed the coefficient of traction (similar to coefficient of friction). It is the force which makes an object move over the surface by overcoming all the resisting forces like friction, normal loads(load acting on the tiers in negative 'Z' axis), air resistance, rolling resistance, etc. Traction can be defined as: a physical process in which a tangential force is transmitted across an interface between two bodies through dry friction or an intervening fluid film resulting in motion, stoppage or the transmission of power. In vehicle dynamics, tractive force is closely related to the terms tractive effort and drawbar pull, though all three terms have different definitions. The coefficient of traction (also, the "coefficient of friction") is defined as the usable force for traction divided by the weight on the running gear (wheels, tracks etc.) i.e.: usable traction = coefficient of traction x normal force Traction between two surfaces depends on several factors: Material composition of each surface. Macroscopic and microscopic shape (texture; macrotexture and microtexture) Normal force pressing contact surfaces together. Contaminants at the material boundary including lubricants and adhesives. Relative motion of tractive surfaces - a sliding object (one in kinetic friction) has less traction than a non-sliding object (one in static friction). Direction of traction relative to some coordinate system - e.g., the available traction of a tire often differs between cornering, accelerating, and braking.