2.7 Kinetic and Static Friction

Describe kinetic friction between two surfaces

• Kinetic friction occurs when two surfaces in contact move relative to each other.
  • i. The kinetic friction force is exerted in a direction opposite to the motion of each surface relative to the other surface.
  • ii. The force of friction between two surfaces does not depend on the size of the surface area of contact.
• The magnitude of the kinetic friction force exerted on an object is the product of the normal force the surface exerts on the object and the coefficient of kinetic friction. R - -- - µ=FFfk k n, elevant equation:
  • i. The coefficient of kinetic friction depends on the material properties of the surfaces that are in contact.
  • ii. Normal force is the perpendicular component of the force exerted on an object by the surface with which it is in contact; it is directed away from the surface.

Describe static friction between two surfaces.

• Static friction may occur between the contacting surfaces of two objects that are not moving relative to each other.
• Static friction adopts the value and direction required to prevent an object from slipping or sliding on a surface. Relevant equation:
  • i. Slipping and sliding refer to situations in which two surfaces are moving relative to each other.
  • ii. There exists a maximum value for which static friction will prevent an object from slipping on a given surface. Derived equation: µ=FFfs sn,, max
• The coefficient of static friction is typically greater than the coefficient of kinetic friction for a given pair of surfaces. AP Physics 1: Algebra-Based Course and Exam Description Force and Translational Dynamics UNIT 2 TOPIC 2.8 Spring Forces | AP Physics 1: Algebra-Based Course and Exam Description