Friction 4 Resistance to relative motion (or impending motion) of two surfaces. Section 2 F Applied Force, F Friction Force, F f

The Friction Force is: Tangent to surfaces in contact. Opposite to the direction of motion (or impending motion). Dependent on the contact force. FfFf F N F W

The Friction Force is: Dependent on the nature of the contacting surfaces. Independent on relative velocity. Independent on the contact area.

The Friction Force Static coefficient of friction,  s F f max =  s N(impending motion) Dynamic coefficient of friction,  k F f =  k N(motion)

Problem 2-1 The shear is used to cut electronic circuit-board. Determine the force exerted onto the board. Consider the friction between the blade and the vertical guide. 6 in 4 in 12 in 25 lb  s =

Problem 2-2 The material handling mechanism shown slides 8 lb packages along a counter. The coefficient of kinetic friction between the package and counter is The collar weighs 1 lb, and the coefficient of kinetic friction between the collar and rod is Determine the instantaneous torque required to operate this mechanism. The weight of the crank and connecting rod are negligible. Also, the mechanism operates at a low speed, so that inertial forces are also negligible..

Problem 2-2 (con’t) 20 in 8 in 3 in 4 in 16 in

Problem 2-5 For the block brake shown, determine the maximum braking torque that can be provided. 18 in 8 in 2 in 10 lbs  k = 0.3  8 in

Belt Friction 4 Belt/rope/cable wraped around a cylinder causes friction Relative motion (or impending relative motion) 

Belt Friction For a flat belt/rope/cable Tension ratio in belt is T1T1 T2T2 N FfFf FBD belt FfFf N  FBD Drum

Problem 2-13 For the band brake shown, determine the maximum braking torque that can be provided 18 in 4 in 2 in 10 lbs  k = 0.3  8 in

Problem 2-14 A flat belt connects a motor sheave to a machine tool sheave. The maximum tension in the belt is 600 lb. Determine the maximum torque that the motor can provide. The static coefficient of friction of the belt on the sheaves is in 16 in 30 0

Industrial V-belts Common for power transmission. 3V5V8V Selection based on speed and hp

Increased friction, as belt wedges into sheave. Tension ratio in belt is V-Belt Friction T1T1 T2T2 2Nsin  /2 FfFf FBD V-belt N N  

Problem 2-15 A V-belt connects sheave A to a machine tool attached to sheave B. The maximum tension in the belt is 600 lb. Determine the maximum torque that the motor can provide. The V-belt has  =32 0. The static coefficient of friction of the belt on the sheaves is in 16 in 30 0

Problem 2-7 For the brake shown, the spring force is 50 lbs. Determine the braking torque, when a load, P, of 10 lbs is applied to the handle. The coefficient of kinetic friction between the pad and the drum is in 4 in 10 in P 15 0  1 in