Tutorial: Flat Friction Engineering 25 Tutorial: Flat Friction Bruce Mayer, PE Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege.edu

Spring-n-Wts on Ramp Two blocks A and B have a weight of 10 lb and 6 lb, respectively. They are resting on the incline for which the coefficients of static friction are µA = 15% and µB = 25%. Determine the incline angle for which both blocks begin to slide. Also find the required stretch or compression in the connecting spring for this to occur. The spring has a stiffness of k = 2 lb/ft. H13e P8-40

Conceptual Analysis Since Block-A has the lower µS value, it will Slide FIRST, thereby PULLING Block-B Down the ramp with it Thus expect the Dual-Block Slip-Angle Take the FBD of both Blocks noting that the Spring Force, FS, will be equal & opposite for both blocks

Conceptual Analysis Note that Motion IMPENDS for BOTH Static-Position Blocks For Block-A The Block Weight Generates 𝐹 𝑓𝐴 = 𝜇 𝑆𝐴 𝑁 𝐴 Which NOT sufficient to stop Block-A from sliding Only the SPRING Pull maintains Block-A in the Static Position For Block-B The Block Wt Does NOT Generate 𝐹 𝑓𝐵 = 𝜇 𝑆𝐵 𝑁 𝐵 ONLY the SPRING Pull puts Block-B in the condition of Impending Motion