ch08 - Engineering Mechanics: Statics Chapter 8: Friction...

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Unformatted text preview: Engineering Mechanics: Statics Chapter 8: Friction 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 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 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 blocks weight W , and the frictional forces act to the left to prevent force P from moving the block to the right 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 8.1 Characteristics of Dry Friction Theory of Dry Friction Equilibrium...
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ch08 - Engineering Mechanics: Statics Chapter 8: Friction...

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