Georgia State University: Friction hyperphysics.phy-astr.gsu.edu http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html normal force Georgia State University: Friction http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html Georgia State University: HyperPhysics: Friction hyperphysics.phy-astr.gsu.edu Hyperphysics: Coefficients of Friction hyperphysics.phy-astr.gsu.edu http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html standard model hyperphysics.phy-astr.gsu.edu gsu.edu gsu.edu http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html HyperPhysics - Friction http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html Force - Georgia State University http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html#rou Hyperphysics: Friction http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html#fri http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html#fri hyperphysics.phy-astr.gsu.edu Friction Concepts http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html coefficient hyperphysics.phy-astr.gsu.edu University of Georgia: Força [em inglês] HyperPhysics - Friction http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html Friction Physics http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html Simple Friction Model hyperphysics.phy-astr.gsu.edu Friction/Frictional Force http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html#fri HyperPhysics - Friction HyperPhysics - Friction http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html roughness of the surfaces coefficient http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html#coe Friction - HyperPhysics http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html standard model