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ES2501: Statics/Unit 24-1 : Friction Related Problems

Introduction. ES2501: Statics/Unit 24-1 : Friction Related Problems. Friction – force of resistance against motion or impending motion on and tangent the contact surface of two bodies. Classification of friction :. against relative motion. Fluid friction.

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ES2501: Statics/Unit 24-1 : Friction Related Problems

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  1. Introduction ES2501: Statics/Unit 24-1: Friction Related Problems Friction – force of resistance against motion or impending motion on and tangent the contact surface of two bodies. Classification of friction: against relative motion Fluid friction Friction Kinetic friction Dry friction Static friction Theories of friction: Several theories exist. For examples: against impending relative motion studied in Statics Impact between two rough surfaces causes friction bonding force between two surfaces causes friction

  2. Law of Dry Friction Friction exists on the contact surface If B moves or has impending motion relative to A B ES2501: Statics/Unit 24-2: Friction Related Problems A Case 1: In Motion ------ Kinetic friction Case 2: Impending Motion ------ static friction Direction of motion relative to A Direction of impending motion trlstivr to A B B Normal pressure of A on B Kinetic Friction of A on B Normal Pressure of A on B Static Friction of A on B static friction coefficient Kinetic friction coefficient Magnitude: Magnitude: Direction: Opposite to the direction of the impeding motion Direction: Opposite to the direction of motion Maximum static friction --- a limit . Not necessarily the true static friction

  3. Angle of Static Friction Static friction can be characterized by either the static friction coefficient of the angle of static friction ES2501: Statics/Unit 24-3: Friction Related Problems Direction of the impeding motion Maximum static Friction Normal Pressure Resultant of friction and pressure

  4. Example 1: ES2501: Statics/Unit 24-4: Friction Related Problems Find the friction force when F=5N and 10N, respectively. FBD: Equilibrium equations: Case 1: Case 2: Note: gives the limit but not true static friction; gives true kinetic friction, Not-satisfied satisfied Static friction Kinetic friction in motion

  5. Example 2:Three concrete pipes of weight W and radius r are stacked on the ground. Determine the minimum static friction coefficient such that the pile doesn’t collapse. A ES2501: Statics/Unit 24-5: Friction Related Problems B C FBD and Equilibrium equations: A C B

  6. Example 3: A wedge of an angle is used to split a log.Find the splitting force when the wedge is hit by P and the force to keep the wedge in the position in the log. ES2501: Statics/Unit 24-6: Friction Related Problems FBD and Equilibrium equations: A Load Friction To advance normal force Wedge angle Splitting force generated by P Force required to keep wedge in position

  7. Example 3: Friction on flat belts ES2501: Statics/Unit 24-7: Friction Related Problems Proof: Small T1 can hold large T2

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