Engineering 25
Tutorial:
Flat
Friction
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering-36: Engineering Mechanics - Statics
1
Bruce Mayer, PE
ENGR36_Tutorial_Flat_Friction_Spring-n-Wts.pptx
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.
Engineering-36: Engineering Mechanics - Statics
2
Bruce Mayer, PE
ENGR36_Tutorial_Flat_Friction_Spring-n-Wts.pptx
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
arctan  A   
 arctan B 
 Take the FBD of both Blocks
noting that the Spring Force,
FS, will be equal & opposite
for both blocks
Engineering-36: Engineering Mechanics - Statics
3
Bruce Mayer, PE
ENGR36_Tutorial_Flat_Friction_Spring-n-Wts.pptx
Engineering-36: Engineering Mechanics - Statics
4
Bruce Mayer, PE
ENGR36_Tutorial_Flat_Friction_Spring-n-Wts.pptx
Engineering-36: Engineering Mechanics - Statics
5
Bruce Mayer, PE
ENGR36_Tutorial_Flat_Friction_Spring-n-Wts.pptx
Engineering-36: Engineering Mechanics - Statics
6
Bruce Mayer, PE
ENGR36_Tutorial_Flat_Friction_Spring-n-Wts.pptx
Engineering-36: Engineering Mechanics - Statics
7
Bruce Mayer, PE
ENGR36_Tutorial_Flat_Friction_Spring-n-Wts.pptx