Characteristics of Dry Friction

Consider a gardener pushing a wheelbarrow. As a force is applied to move the cart, dry friction develops between the wheel and the ground.

The static frictional force acts tangential to the contact surface, opposite to the force about to cause a motion.

When the wheelbarrow is about to slip, the maximum static frictional force at the interface is proportional to the normal force. Here the coefficient of static friction depends on the types of materials in contact and the roughness of the surfaces.

The static frictional force is independent of the contact area only when the normal pressure is within a specific range that does not cause deformation or damage to the contacting surfaces.

When the wheelbarrow starts slipping, the developed kinetic frictional force is proportional to the normal force.

It is generally lower than the maximum static frictional force. However, if the cart moves with a very low velocity over the surface, they become approximately equal.

The coefficient of kinetic friction generally depends on the material's surface properties and the surrounding environment.