ECS221L22

# ECS221L22 - APPLICATIONS OF FRICTION Wedges Square Threaded...

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APPLICATIONS OF FRICTION Wedges Square Threaded Screws Thrust Bearings Wheel Friction

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Wedges Wedges are used to raise heavy loads by small amounts. P A What is the minimum value of force P required to raise block A?
Analysis Free body diagrams. A W N 2 N 1 μ s N 2 μ s N 1 P μ s N 2 N 2 N 3 μ s N 3 4 equilibrium equations for N 1 , N 2 , N 3 , P.

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Square Threaded Screws The jack. W P a 2r
Block-On-Inclined Plane Analogy Unwrap thread of base (2 π r). In one turn, screw is raised vertically amount L (the lead). lead angle: friction angle: θ L 2 π r Q W θ φ s R θ =tan -1 L/2 π r Impending slip upwards! φ =tan -1 μ s

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Equilibrium F x =0 Q = R sin (θ +φ s 29 F y =0 W = R cos (θ +φ s 29 Relate P to Q. L 2 π r θ Q W θ φ s R Qr=Pa , P=Qr/a Q = W tan( θ + φ s ) W P a 2r
Self-Locking Screws Self-locking if weight remains in place when force P is removed.

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ECS221L22 - APPLICATIONS OF FRICTION Wedges Square Threaded...

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