friction force and centrifugal force notes Static Friction

Friction is a contact force that opposes the relative motion or the tendency of motion between two surfaces in contact.

Types of Friction

(a) Static Friction

• Acts when there is no relative motion.

• Adjusts itself according to applied force.

• Has a maximum value called limiting friction.

• Responsible for walking, rolling without slipping, etc.

(b) Kinetic (Sliding) Friction

• Acts when surfaces slide over each other.

• Constant in magnitude for given surfaces.

• Less than maximum static friction.

(c) Rolling Friction

• Acts during rolling motion.

• Much smaller than sliding friction.

• Friction opposes relative motion, not applied force.

  Example:

  • If a car accelerates forward, friction on tires acts forward.

  • If a block is about to slide down an incline, friction acts up the incline.