Friction

Definition

Friction is the resistive force that occurs when two surfaces interact, opposing the relative motion between them. It acts parallel to the surfaces in contact and can be either static or kinetic.

5 Must Know Facts For Your Next Test

1. Friction depends on the nature of the surfaces in contact and the normal force pressing them together.
2. Static friction prevents objects from starting to move and is generally greater than kinetic friction, which opposes ongoing motion.
3. The coefficient of friction ($\mu$) is a dimensionless quantity representing the ratio of frictional force to normal force; it varies for static ($\mu_s$) and kinetic ($\mu_k$) friction.
4. The formula for calculating frictional force is $f = \mu N$, where $N$ is the normal force.
5. Friction converts kinetic energy into thermal energy, leading to wear and heat generation at contact points.

Review Questions

• What is the difference between static and kinetic friction?
• How does increasing the normal force affect the frictional force between two surfaces?
• Explain how the coefficient of friction influences the magnitude of frictional forces.

Related terms

Normal Force:

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

Coefficient of Friction:

$\mu$, a dimensionless constant that represents the ratio of frictional force to normal force for specific materials.

Kinetic Energy:

Energy possessed by an object due to its motion, calculated as $KE = \frac{1}{2}mv^2$.