Coefficient of kinetic friction

Definition

The coefficient of kinetic friction is a dimensionless constant that represents the ratio of the force of kinetic friction between two bodies in relative motion to the normal force pressing them together. It is denoted by $\mu_k$.

5 Must Know Facts For Your Next Test

1. The coefficient of kinetic friction ($\mu_k$) is always less than or equal to the coefficient of static friction ($\mu_s$).
2. It depends on the materials in contact and their surface properties, but not on the area of contact.
3. The force of kinetic friction can be calculated using $f_k = \mu_k N$, where $N$ is the normal force.
4. Unlike static friction, kinetic friction remains constant regardless of the speed of sliding.
5. Typical values for $\mu_k$ range from close to zero (for very smooth surfaces) to just under one (for rough surfaces).

Review Questions

• What does the coefficient of kinetic friction represent?
• How do you calculate the force of kinetic friction?
• Why is the coefficient of kinetic friction usually less than the coefficient of static friction?

Related terms

Static Friction:

The force that resists the initiation of sliding motion between two surfaces in contact. It must be overcome for motion to start.

Normal Force:

The perpendicular force exerted by a surface against an object resting on it, denoted as $N$.

$f_k = \mu_k N$: $f_k = \mu_k N$ is the formula used to calculate the force of kinetic friction, where $f_k$ is the kinetic frictional force, $\mu_k$ is the coefficient of kinetic friction, and $N$ is the normal force.