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# ch08 - Chapter8 Friction :Statics ChapterObjectives...

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Engineering Mechanics: Statics Chapter 8:  Friction

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Chapter Objectives To introduce the concept of dry friction and  show how to analyze the equilibrium of rigid  bodies subjected to this force. To present specific applications of frictional  force analysis on wedges, screws, belts, and  bearings. To investigate the concept of rolling resistance.
Chapter Outline Characteristics of Dry Friction Problems Involving Dry Friction Wedges Frictional Forces on Screws Frictional Forces on Flat Belts Frictional Forces on Collar Bearings, Pivot  Bearings, and Disks Frictional Forces on Journal Bearings Rolling Friction

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8.1  Characteristics of Dry  Friction Friction  or retards slipping of the body relative to a  second body or surface which it is in contact Acts tangent to the surfaces at points of contact  with other body Opposing possible or existing motion of the body  relative to points of contact Two types of friction – Fluid and Coulomb  Friction
8.1  Characteristics of Dry  Friction Fluid friction  exist when the contacting  surface are separated by a film of fluid  (gas or liquid) Depends on velocity of the fluid and its  ability to resist shear force  Coulomb friction , also known as dry  friction, occurs between contacting  surfaces of bodies in the absence of a  lubricating fluid

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8.1  Characteristics of Dry  Friction Theory of Dry Friction Consider the effects caused by pulling  horizontally on a block of uniform weight  W  which  is resting on a rough horizontal surface Consider the surfaces of  contact to be nonrigid or  deformable and other parts  of the block to be rigid
8.1  Characteristics of Dry  Friction Theory of Dry Friction FBD of the block The floor exerts a distribution of  the normal force  N n  and frictional  force  F n  along the contact  surface For equilibrium, the normal forces  act upward to balance the block’s  weight  W , and the frictional forces  act to the left to prevent force  P   from moving the block to the right

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8.1  Characteristics of Dry  Friction Theory of Dry Friction Examining the contacting surfaces between  the floor and the block, it can seen that many  microscopic irregularities exist between the  two surfaces Reactive forces  R n  developed at each of  the protuberances
8.1  Characteristics of Dry  Friction Theory of Dry Friction These forces act at all points of contact  and each reactive force consist of both  a frictional component  F n  and a  normal component  N n

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8.1  Characteristics of Dry  Friction Theory of Dry Friction Equilibrium
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