Friction (Chapter 7) - Key Terms and Concepts

A vocabulary set covering definitions and key concepts related to friction, its types, factors affecting it, methods to reduce it, and its advantages and disadvantages.

Friction

The resistive contact force that opposes the motion or tendency of motion between two surfaces in contact.

Frictional force

The force that arises at the contact between surfaces and opposes their relative motion.

Static friction

Friction that acts between surfaces in contact when there is no relative motion, preventing initiation of motion.

Limiting friction

The maximum static friction just before motion begins; the force required to start moving a stationary object.

Sliding friction

Friction between two surfaces when one slides over the other; opposes the motion of the moving object.

Rolling friction

Resistance experienced when a body rolls over a surface; typically smaller than sliding friction.

Fluid friction

Friction that occurs in fluids (air or water); also called drag, opposing motion through the fluid.

Drag

The fluid friction force acting on a body moving through a fluid.

Factors affecting friction – nature of the surface

Rougher surfaces increase friction; smoother surfaces reduce friction.

Factors affecting friction – weight of the body

Friction increases as the weight (normal force) pressing the surfaces together increases.

Oiling (Lubrication)

Applying oil to surfaces to reduce friction by smoothing contact between surfaces.

Polishing

Smoothing rough surfaces to reduce friction by making contact smoother.

Streamlining

Shaping objects to reduce resistance from air or water, thereby reducing fluid friction.

Anti-friction alloys

Special alloys used to line moving parts, reducing sliding friction between surfaces.

Air cushions

A thin film of compressed air between surfaces that greatly reduces friction (as in hovercrafts).

Ball bearings

Small rolling elements placed between moving parts to convert sliding friction into rolling friction and reduce overall friction.

Advantages of friction

Friction enables walking, grip, writing, and holding objects; it prevents slipping.

Disadvantages of friction

Causes wear and tear, produces heat, wastes energy, and reduces efficiency of machines.