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Friction

Friction. Don’t rub me the wrong way!. Friction Theory . Arises from two objects in “contact”, where “contact” is made with: Surface imperfections: asperites , micro-cracks, other Inter-particle attractions: adhesion, other Other other ?. Kinds of friction. Static

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Friction

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  1. Friction Don’t rub me the wrong way!

  2. Friction Theory Arises from two objects in “contact”, where “contact” is made with: • Surface imperfections: asperites, micro-cracks, other • Inter-particle attractions: adhesion, other • Other other?

  3. Kinds of friction • Static • Exists between two surfaces that are NOT moving relative to each other • Kinetic • Exists between two surfaces that ARE moving relative to each other • In most cases, less than static • Rolling • Air Resistance • Fluid flowing around an object

  4. Coefficient of Friction μ– “mu” – small Greek letter M - symbol for coefficient of friction • A numerical value that describes the nature of the “contact” surfaces • Determined experimentally. • Not constant over a wide range of relative velocities • May or may not depend on surface area

  5. Friction Force Proportional to the Normal Force • Ff = μs FN Magnitude of frictional force due to static friction • Static Coefficient of Friction: μs • Ff = μk FN Magnitude of frictional force due to kinetic friction • Kinetic Coefficient of Friction: μk

  6. Coefficients of friction • To determine static μsFind maximum angle on an incline where velocity = 0 • To determine kineticμk Find maximum angle on an incline where velocity = constant

  7. Tribology • Contact Mechanicsof Moving Interfaces • Generally involves energy dissipation • Also encompasses the science fields of: • Adhesion • Friction • Lubrication • Wear

  8. Demo: Let’s make it work

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