Dry friction or solid friction is called Coulomb friction. Here no lubricant is used between two contacting surfaces.
5.6.1 Laws of Coulomb Friction
a) The frictional force acts in the opposite direction of the surface having tendency to move.
b) The force of friction is equal to the applied force so long the surface is at rest.
c) When the surface is on the verge of sliding, the force of friction is maximum and this maximum frictional force is termed as limiting friction force.
d) The limiting frictional force bears a constant ratio to the normal reaction between two surfaces.
e) The limiting frictional force does not depend upon the shape and areas of the surfaces in contact
f) The coefficient of kinetic friction is less than the coefficient of static friction