Sec. 5-3 Friction forces x Friction is the force that oppose(反抗)the relative motion or the trend of relative motion of two solid surfaces in contact static friction Friction sliding friction V kinetic friction rolling Triction 1) The forces of static friction(静摩擦力) The frictional forces acting between surfaces at rest with respect to each otherSec. 5-3 Friction forces ★ Friction is the force that opposes (反抗) the relative motion or the trend of relative motion of two solid surfaces in contact Friction static friction kinetic friction sliding friction rolling friction √ ➢1) The forces of static friction (静摩擦力) The frictional forces acting between surfaces at rest with respect to each other