Friction Wedges & Screws ENGR B36 - Statics Pat Aderhold 11/24/2014

News & Notes

News & Notes

Today’s Agenda More friction... Practice Problems on white board Wedges Screws Practice Problems on white board Review / project time

Working with Wedges Nothing new Text emphasizes graphical solutions Same use of F = µN Same equilibrium equations Text emphasizes graphical solutions Easier to work with “friction angle” φ µ = tanφ Resultant “inclined from normal” by this amount

Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 357 Working with Wedges Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 357

(That we aren’t going to concern ourselves with) 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.

Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 363 Practice Problem 6/53 The 10° wedge is drive under the spring-loaded wheel whose supporting strut C is fixed. Determine the minimum coefficient of static friction µs for which the wedge will remain in place. Neglect all friction associated with the wheel. Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 363

Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 363 Practice Problem 6/56 The 10° doorstop is inserted with a rightward horizontal force of 30 lb. If the coefficient of static friction for all surfaces is µs = 0.20, determine the values NU and NL 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? Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 363

Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 359 Screws Many applications Derive basic equation on white board Square threads Jack with load W and moment M Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 359

“Unwrapping” the Screw Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 360

Scenarios With At “on the verge of unwinding” Raising the load Lowering the load Screw unwinds itself Can prevent by adding moment At “on the verge of unwinding”

Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 365 Practice Problem 6/62 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. Meriam, JL and Kraige, LG. Statics 7th Ed. Wiley 2012. p. 365

For Exam #3 Can fill out a note card Three problems Up to 4” x 6” One side only Bring to me for approval on Wednesday Three problems Distributed loading / shear & moment diagrams Buoyancy Friction

Group Design Project due next Wednesday! For Next Class Read 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!

Open Time Ask individual questions on HW Work on group design project