Friction

Free-body diagram for a block on a ramp. Arrows are vectors indicating directions and magnitudes of forces. N is the normal force, mg is the force of gravity, and F_f is the force of friction.

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Friction is desirable and important in supplying traction to facilitate motion on land. Most land vehicles rely on friction for acceleration, deceleration and changing direction. Sudden reductions in traction can cause loss of control and accidents. Friction is not itself a fundamental force. Dry friction arises from a combination of inter-surface adhesion, surface roughness, surface deformation, and surface contamination. The complexity of these interactions makes the calculation of friction from first principles impractical and necessitates the use of empirical methods for analysis and the development of theory. Friction is a non-conservative force (work done against friction is path dependent). In the presence of friction, some kinetic energy is always transformed to thermal energy, so mechanical energy is not conserved.

Dependencies

• Friction
  • Bow drill
  • Hand drill
  • Pump drill

See also

• Energy
• Gravity
• Inclined Plane
• Wedge

References

This article uses material from the Wikipedia article Friction, which is released under the Creative Commons Attribution-ShareAlike 3.0 Unported License (view authors).