Coefficient of static friction

Definition

The coefficient of static friction is a dimensionless scalar that represents the ratio of the maximum static frictional force between two surfaces to the normal force pressing them together. It quantifies how difficult it is to start moving an object at rest.

5 Must Know Facts For Your Next Test

1. The coefficient of static friction is typically denoted by the symbol $\mu_s$.
2. It has no units because it is a ratio of forces.
3. The value of $\mu_s$ depends on the materials and surface textures in contact.
4. $f_s \leq \mu_s N$, where $f_s$ is the static frictional force and $N$ is the normal force.
5. When an object starts moving, kinetic friction takes over, which generally has a lower coefficient than static friction.

Review Questions

• What does the coefficient of static friction quantify?
• What is the typical symbol used for the coefficient of static friction?
• How does the coefficient of static friction compare to kinetic friction for most material pairs?

Related terms

Static Friction:

The force that resists the initiation of sliding motion between two surfaces in contact.

Kinetic Friction:

The force that opposes the relative motion or sliding between surfaces in contact once they are already moving.

Normal Force:

The perpendicular contact force exerted by a surface on an object in contact with it.