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ContactForces3

# ContactForces3 - Types of forces Free-body Diagrams Contact...

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Types of forces Free-body Diagrams Contact Forces: Normal force: to contact surface ! N Frictional force: || to contact surface ! f ! f ! ! N Simulation: The Ramp look at forces on box when the incline angle is increased two types of friction: ! f s : static (no slipping) and ! f k : kinetic (slipping) coefficients of friction: μ s and μ k o μ s approximately 25% higher than μ k o μ s and μ k depend on the materials in contact F g : interaction pair = box + Earth f s : interaction pair = box + ramp N: interaction pair = box + ramp f static exists because the box tends to slide down the ramp. When θ = 0, f s = 0 no tendancy to slide – no frictional force Part of the weight is working to push the mass down the ramp: mg parallel Part of the weight keeps the box in contact with the ramp: mg normal o Resolve the weight vector into these components F g = mg = hypotenuse of right triangle with vertex angle = θ mg parallel = side opposite of θ = mg sin ! mg normal = side adjacent to θ = mg cos !

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Types of forces Free-body Diagrams Block not accelerating forces are balanced f s = mg sin ! N = mg cos ! As θ increases mg sin ! increases f s increases θ max = angle when the box starts to slide ! f s = f s ,max ! f s ! μ s ! N !
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