Chapter 6

Notes

Chapter 6 Force and Motion II Chapter Goal: To use Newton’s laws to solve equilibrium and dynamics problems with regard to friction, drag and circular motion. 1 Friction Static Friction 𝑓 𝑠 (static means stationary, no sliding) ➢ Keeps the box from slipping. ➢ Opposes the direction of the intended slide direction. ➢ Rises from zero to some maximum value: 0 < 𝑓 𝑠 < 𝑓 𝑠 𝑚𝑎𝑥 Ch. 6.1 2 When box is on the verge of slipping, friction is at its maximum 𝒇 𝒔 𝒎𝒂𝒙 . 𝒗 = 𝟎 𝒗 = 𝟎 𝒗 = 𝟎 𝒗 = 𝟎 Friction Kinetic Friction 𝑓 𝑘 (sliding is occurring) Once object “breaks free”, sliding occurs. ➢ Opposes the direction of the slide. ➢ Magnitude is less than the maximum static friction. Ch. 6.1 3 Box is sliding leftward therefore kinetic friction 𝒇 𝒌 is opposing the sliding motion. Ԧ 𝑎 Friction Simplified View of Friction Mechanisms ➢ Surfaces are not smooth. ❑ When surfaces touch, a relatively small number of points make contact (relative to the billions of possible contact points). ▪ Bonds form at these contact points (Van der Waals forces). ❑ If you attempt to slide one surface across another, the bonds (and physical interference) oppose this attempt. Ch. 6.1 Push top surf...