Wedges amp Screws ENGR B36 Statics Pat Aderhold 11242014 News amp Notes News amp Notes Todays Agenda More friction Wedges Screws Practice Problems on white board Review project time ID: 270390
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Slide1
FrictionWedges & Screws
ENGR B36 - Statics
Pat Aderhold
11/24/2014Slide2
News & NotesSlide3
News & NotesSlide4
Today’s AgendaMore friction...WedgesScrewsPractice Problems on white board
Review / project timeSlide5
Working with WedgesNothing newSame use of F = µNSame equilibrium equationsText emphasizes graphical solutions
Easier to work with “friction angle”
φ
µ
=
tanφ
Resultant “inclined from normal” by this amountSlide6
Working with Wedges
Meriam
, JL and
Kraige
, LG. Statics 7
th
Ed. Wiley 2012.
p.
357Slide7
Other Details(That we aren’t going to concern ourselves with)Sliding and locking
Slides only if slip
simultaneously
top & bottom
Otherwise “self-locking”
No slip if
Pull out from locked position?
Friction opposite direction
Just another set of FBDs and
equil
. eqns.Slide8
Practice Problem 6/53Meriam, JL and
Kraige
, LG. Statics 7
th
Ed. Wiley 2012.
p.
363
The 10° wedge is drive under the spring-loaded wheel whose supporting strut C is fixed. Determine the minimum coefficient of static friction
µ
s
for which the wedge will remain in place. Neglect all friction associated with the wheel.Slide9
Practice Problem 6/56Meriam, JL and
Kraige
, LG. Statics 7
th
Ed. Wiley 2012.
p.
363
The 10° doorstop is inserted with a rightward horizontal force of 30 lb. If the coefficient of static friction
for all surfaces is µ
s
= 0.20, determine the values
N
U
and
N
L
of the normal forces on the upper and lower faces of the doorstop. With the given information, can you determine the force
P
required to extract the doorstop?Slide10
ScrewsMany applicationsDerive basic equation on white boardSquare threadsJack with load W and
moment M
Meriam
, JL and
Kraige
, LG. Statics 7
th
Ed. Wiley 2012.
p.
359Slide11
“Unwrapping” the Screw
Meriam
, JL and
Kraige
, LG. Statics 7
th
Ed. Wiley 2012.
p.
360Slide12
ScenariosWith Raising the loadLowering the load
With
Screw unwinds itself
Can prevent by adding moment
At “on the verge of unwinding”Slide13
Practice Problem 6/62Meriam, JL and
Kraige
, LG. Statics 7
th
Ed. Wiley 2012.
p.
365
Determine the torque M which must be applied to the handle of the screw to begin moving the 100
lb
block up the 15° incline. The coefficient of static friction between the block and the incline is 0.50 and the single-thread screw has square threads with a mean diameter of 1 in. and advances 0.4 in. for each complete turn. The coefficient of static friction for the threads is also 0.50. Neglect friction at the small ball joint A.Slide14
For Exam #3Can fill out a note cardUp to 4” x 6”One side only
Bring to me for approval on Wednesday
Three problems
Distributed loading / shear & moment diagrams
Buoyancy
FrictionSlide15
For Next ClassRead through Articles A1 &
A2
Practice Problems 6
/63
&
6/66
Think of questions and review problems
Make/bring “cheat sheet” for Exam #3
Exam
#3 next Monday!
Group Design Project due next Wednesday!Slide16
Open TimeAsk individual questions on HWWork on group design project