http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html#ass http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html#vel http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html#ass http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html#ass Friction and area of contact http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html#are http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html