enme110_lecture_22

# enme110_lecture_22 - CHAPTER 8 FRICTION Wedges Wedges are...

This preview shows pages 1–9. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: CHAPTER 8 FRICTION Wedges Wedges are inclined planes used to increase the application of a force. The two force equilibrium equations are used to relate the 'forces acting on the wedge. An‘applied force P must push on the wedge to move it to the right. If the coefficients of friction between the surfaces are large enough, then P can be removed, and the wedge will be self-locking and remain in place. Screws Square-threaded screws are used to move heavy loads. They represent an inclined plane, wrapped around ‘a cylinder: ' 7 The moment needed to turn a screw . depends upon the coefﬁcient of friction and the screw’s lead angle 9. , If the coefficient of friction between the surfaces is large enough, then the screw - will support the load without tending to turn, i'.e_., it will be self-locking. Flat Belts The force'needed to move a flat belt over a rough curved surface depends only on the angle of belt contact, [3, and the coefficient of friction. M = Wr tan(6 + 4):) Upward Impending Screw Motion M‘ = Wrtan(9 — (:55) Downward Impending Screw Motion. 9>¢9 i M” = Wr tan(qb — 5) _ Downward Screw Motion #5: > 9 Motion or impending motion of belt relative to surface _,_.__.—.-...._ NR ~l50» Collar Bearings and Disks The frictional analysis of a collar bearing or disk requires looking at a differential element of the contact area. The normal force acting on this element is determined frOm force equilibrium along the shaft, and the moment needed .to turn the shaft at a constant rate'is determined from moment equilibrium ‘ about the shaft’s axis. If the pressure on the surface of a collar bearing is uniform, then integration gives the result shown. . Journal Bearings When a moment is applied to a shaft in a nonlubricated or partially lubricated journal bearing, the shaft will tend to roll up the side of the bearing until slipping occurs This defines the radius of a friction circle, and from it the moment needed to turn the shaft can be determined. I Rolling Resistance The resistance of a wheel to rolling over a surface is caused by localized deformation of the two materials in Contact. This causes the resultant normal force acting on the rolling body to be inclined so that it provides a component that acts in the opposite direction of the applied force P causing the motion.'Ihis effect is characterized using the Coefﬁcient of rolling resistance, a, which is determined from experiment. M = Rr sin (bk QiMA;¢ Mr W (Riga-359 Z W'Cb' 'P.~r'_".’wei.. A- pproxi Maire...” “\JWEON“ CHAPTER REVIEW Rotation 15!» .—..—. ,, I. gL‘naoswery a . . ._._..... n e. , .o :MQ , .. ,, ,, ,%.&n.eca\, ,o A, C056 “‘1'? '“M' > (WW: Q:Q,,\$,,a , , ,, . 5%, w N, a 7 7 ".7 _ .. _. .. , , (, . ‘ «453-— 1 2 i :ﬁeluﬁsvt (weiae. <:x,s..:s‘n5~**£’n-L kale.ng \FQntﬁvaJ) .. ‘ 7 __ _ 5 , ._ _. 7 ,, _e.__,_ﬂ_+,,w\2£_l\3~g£49587w M 2;, ,3; , ,, ............. ._ 7 H ‘ .. . 7 N .. __ __ ._ 5.1,L‘VQW {1,2 z: 7 4.". WM Mogaer Mg}. _. __ , 7 . .. __ +7 1:959 ,, _. gProHem ~ “3.15 I1 |.1 Pro, .. , ,,.:.:.V.g p A;V\s%:, @4453»; ."ojs‘ _. . _, ,, , :_._ . . ‘jéjzﬁé “£5 Mmgfﬁgxcogaﬂ44?, 77:75:37, ,, ,, ,, , J ‘ "ff—{>7 . ﬁguﬂgﬁsinﬂuw g: a" t.) 7 W Ua-ov/COSQh/z'zS/iﬂﬂjzi M; 3 {79, [’19) .2‘ .I’ _. ._ . E i H. .. ._ 77/7790.” a.../._ _. _ FF. Orb._.._.._.._:. "41.174; 7 7, , , \ " " " ~_ ._ .. f, ) ‘ _ ._ “ ifeCa't‘{9 v\ 3 . C; (D .— \SV-u I—l-l—lI—|-|-—'-HHHI—ll-‘HHI—Ll—LI—lHl—LHHHMI—Li—‘I—ll—lHI—‘HHS—LHHHl—ll—lI—LHH 999999999-9999999099999999900009000099000000000 I—‘l—‘I—lI—LI—I-i—Llr-d-i-l-J-L Theta De ‘ Teta __ F 1 0.017453292 -3.51395553 2 0034906584. -2822706 3 0052359877 -24192401 4 0.069813169 —2.13365883 5 0.087266461 -1.91271773 6 0.104719753 -1.73270031 7 0.122173046 —1 58095553 8 0.139626338 -1.44993189 9 0.15707963 -133475854 10 0 174532922 -1.23210975 11 0.191986214 -1 13961346 12 0.209439507 —1 05551827 13 0 226892799 —0.97849418 14 0 244346091 -0 90750743 15 0261799383 —084173853 16 0.279252676 —0.78052694 17 0.296705968 —0.72333239 18 0.31415926 '-0.6697074 19 0.331612552 -o.61927718 20 50.349065844 —o.5717247 21 0.366519137 -0.52677941 22 0.383972429 ~O.4842086 23 '0401425721 ~0A4381064 24 0418879013-—0A0540974 25 0436332306.—036885166 26 (L453785598 -0.33400039 27 047123889 4130073536 28 04886921823—026894923 29 0.506145474 -0 23854601 30 0.523598767 -0 20943952 31 0.541052059 -0.18155212 32 0 558505351 -0 15481362 33 0.575958643--0.12916035 34 0.593411936 -0 10453444 35 ‘0.610865228;—0.08088306 36 .o.62831852 —0.05815793 37 0.645771812I -0 0363148 _: 1 Qﬁﬁﬁﬂgé;gﬁ,;191531229 é_—~mwm w. 8048891 “8) >8 40 .o.698131689 0.024313447 41 20715584981 0843004528 42 _0 733038273 0.060987698 43 .0 750491566 0.078290355 44 ‘0.767944858 0.094937944 45 _0.78539815 0.110954132 46 '0802851442;0.126360962 47 0 820304734 0.141178988 48 *0.837758027;0.155427402 ;. ‘l 3| CLA m f0 1/ M3. i..._b:-{zmrz_.¢c: 4-. A ﬁ ! E H . ' ‘ E ﬁg Uiﬁlﬁ \ a? __ _ b. 1;? ,7 .. h ,, ,, - I (é _ _hn_m ;" WWW ”_mm,mm"Wmmmwwmmww€iwwﬂw,wmmmmMWWHWMMH , ,, 19:90 \$143an _ ...
View Full Document

{[ snackBarMessage ]}

### Page1 / 9

enme110_lecture_22 - CHAPTER 8 FRICTION Wedges Wedges are...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online