Force Problems involving Friction

What is Friction? It is a force that opposes motion.

Friction is caused by the contact (rubbing) of 2 surfaces.

The roughness of the surfaces involved is related to amount of friction. This goes to the atomic level.

When drawing a vector for friction, it should always point in the direction opposite of the movement.

The Direction of Friction

Friction and the Normal Force

When the normal force

increases, the area of contact

between the two objects

also increases,

This causes the frictional force to increase as

well.

Static and Kinetic Static friction (fs) refers to an object

that is moving. It does two things: Prevents an object from moving (sliding)

Resists the initiation of movement

Static friction is usually stronger than kinetic friction.

Kinetic friction (fk)refers to the force friction on an object in motion. There are two types: sliding and rolling.

The Coefficient of Friction The coefficient of friction (μ) is the ratio of

the frictional force divided by the normal force.

It increases for rougher surfaces, and decreases for smoother surfaces.

It has no unit of measurement.

μ = f/FN

f = μFN