Physical Education · Ch 8 — Biomechanics and Sports
Types of Friction
Types of Friction
Types of Friction
Friction is grouped into two broad kinds — static friction and kinetic friction — and kinetic friction is itself of three types. Knowing which is at work in a given sport is a common question in CBSE Class 12 Physical Education exams.
Static Friction
Static friction acts when the force applied to an object is not enough to make it move. Because of static friction you must use extra force to start a stationary object moving: if you push a heavy object with less force than the static friction between it and the floor, it stays put, and only a push greater than the static friction will set it going. Once the object is actually moving, there is no longer any static friction.
Kinetic Friction
Kinetic friction acts once a force has set an object moving. It includes three different types:
- (a) Sliding friction — when two bodies are in contact and one slides or rubs over the surface of the other. Examples: skating on ice, planting the pole in the pole vault, and skiing or sliding a weight.
- (b) Rolling friction — when one body rolls over the surface of another, as a wheel does. Example: a struck hockey or cricket ball rolls ahead and, after a while, friction brings it to rest; roller skates and skateboards also depend on rolling friction.
- (c) Fluid friction — the resistance that opposes motion through a fluid (gas, air or water). Examples: the air resistance you feel while riding a bike; cyclists wear streamlined helmets and specially designed clothing to cut fluid friction; and the glide of a paraglider or hang-glider through the air.