A force that resists motion between two objects in contact Friction results in the conversion of mechanical energy into waste heat that dissipates into the surrounding environment
resistance to the motion of one surface over another The amount of friction is dependent on the smoothness of the contacting surfaces, as well as the force with which they are pressed together Friction between unlubricated solid bodies is independent of speed and area The coefficient of friction is obtained by dividing the force required to move one body over a horizontal surface at constant speed by weight of the body Coefficients of rolling friction (e g , the motion of a tire or ball bearing) are much less than the coefficient of sliding friction (back and forth motion over two flat surfaces) Sliding friction is thus more wasteful of energy and can cause more wear Fluid friction occurs between the molecules of a gas or liquid in motion, and is expressed as shear stress Unlike solid friction, fluid friction varies with speed and area In general, lubrication is the substitution of low fluid friction in place of high solid-to-solid friction See tribology
When one object rubs against another Friction reduced the energy and slows down the pendulum In a pendulum, the friction is between the bob and the air
a rubbing, esp of one object against another Mechanics: The resistance to motion of two moving objects or surfaces that touch Tribology: The resisting force encouraged at the common boundary between two bodies when, under the action of an external force, one body moves or tends to move relative to the other [<French < Latin frictio < pp of fricare, to rub] FZG test