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Rolling resistance is the force resisting the motion when a body rolls on a surface, mainly caused by non-elastic effects such as hysteresis and deformation. Learn how rolling resistance depends on wheel diameter, load, surface adhesion, and material properties, and how it affects vehicles and trains.
The proportionality coefficient is the dimensionless "Darcy friction factor" or "flow coefficient". This dimensionless coefficient will be a combination of geometric factors such as π, the Reynolds number and (outside the laminar regime) the relative roughness of the pipe (the ratio of the roughness height to the hydraulic diameter).
Learn how to calculate the Darcy friction factor for different flow regimes using various equations, including the Colebrook–White equation for turbulent flow in rough pipes. The Colebrook–White equation is an implicit equation that can be solved numerically or with explicit reformulations.
The Moody chart or Moody diagram is a graph that relates the Darcy–Weisbach friction factor, Reynolds number and surface roughness for fully developed flow in a circular pipe. It can be used to predict pressure drop or flow rate down such a pipe and is based on experimental data and theoretical analysis.
Stokes' law is an empirical law for the frictional force exerted on spherical objects with very small Reynolds numbers in a viscous fluid. It is used to calculate the terminal velocity of spheres falling in a fluid, such as raindrops or sperm, and to measure the viscosity of fluids using a falling-sphere viscometer.
Learn the definition, formula and application of Fanning friction factor, a dimensionless number used in continuum mechanics calculations. Compare it with Darcy friction factor and see examples for different flow regimes and pipe geometries.
Learn how to calculate the force gain of a flexible line wound around a cylinder, such as a capstan, winch or belt drive. The capstan equation relates the tension, friction, angle and number of turns of the line.
Traction is a force that generates motion between a body and a surface, using friction or shear force. Learn about the factors affecting traction, the coefficient of traction, and the applications of traction in vehicles and engineering design.