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Chapter 5 Notes

Chapter 5 Notes - Chapter 5 Notes Transparency Text 3 Part...

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Chapter 5 Notes Transparency Text 3 Part 2 - Friction o Resistance to motion when object in contact with a surface or viscous medium (e.g. water, air) Results from interactions between object and its environment o Manifest as a force against the direction of motion It wants to accelerate the object in the opposite direction of its motion so it stops o Force of friction o Friction II Two types of friction Static friction o Resistance to getting the object to move Kinetic friction o Resistance the object feels when it is already moving Force of static friction > force of kinetic friction Force of friction proportional to normal force μs coefficient of static friction o fS μS n μk coefficient of kinetic friction o = fk μk n Coefficients depend on the materials in contact Above relations express magnitude, not direction? o Friction III The direction of the frictional force is opposite the direction of motion and parallel to the surfaces in contact The coefficients of friction are nearly independent of the area of contact o Static Friction Static friction acts to keep the object from moving If F increases, so does f s If F decreases, so does f s fs μs n where the equality holds when the surfaces are on the verge of slipping Called impending motion o Kinetic Friction The force of kinetic friction acts when the object is in motion

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Although μ k can vary with speed, we shall neglect any such variation Magnitude f k = μ k n o Friction and Newton’s Laws Friction is a force! Include it in the free-body diagram as part of the ΣF The rules of friction It opposes motion, proportional to normal force Allows us to determine direction and magnitude of frictional force - Uniform Circular Motion o The motion an object moving along a circular path with constant speed
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