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Where the Rubber Meets the Road

Where the Rubber Meets the Road. Friction. Friction. A force that causes surfaces to STICK TOGETHER. Ways to minimize friction. SMOOTH THE SURFACES. LUBRICATION. At the MICROSCOPIC level, most surfaces are very BUMPY and IRREGULAR. Coefficient of Friction.

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Where the Rubber Meets the Road

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  1. Where the Rubber Meets the Road Friction

  2. Friction A force that causes surfaces to STICK TOGETHER Ways to minimize friction SMOOTH THE SURFACES LUBRICATION At the MICROSCOPIC level, most surfaces are very BUMPY and IRREGULAR

  3. Coefficient of Friction • How much materials STICK TOGETHER • Represented by the Greek letter: µ (mu) • DIMENSIONLESS (no units) • The HIGHER the coefficient, the MORE two surfaces STICK TOGETHER

  4. Two Types of Friction • Static Friction – µs • STATIONARY OBJECTS • KEEPS OBJECTS IN PLACE • Kinetic Friction – µk • MOVING OBJECTS • OPPOSES MOTION • Static Friction > Kinetic Friction

  5. Coefficient of Friction • Where can you find a list of Coefficients of Friction? • Your Reference Table! • WHERE??? • Front page, on the bottom right hand corner.

  6. Coefficient of Friction • BE CAREFUL! • Pay attention to the MATERIALS in the problem and if the object is MOVING or STATIONARY! • Different materials have different coefficients of friction.

  7. Calculating Friction Force • Amount of friction depends on: • Coefficient of friction • Static – the object is on top of a surface and motionless • Kinetic– the object is sliding across a surface • Normal Force • Large normal force = MORE friction

  8. Example #1 • A 60 kilogram skier is sliding along a horizontal patch of snow with constant speed. How much force must he supply to continue moving with this constant velocity? We need to know the force of kinetic friction. Since he is moving with CONSTANT SPEED, then FA = Ff

  9. Example #2 • A wooden 15 kilogram block is motionless on a wooden table. • A force of 100 Newtons is now applied to the block. Calculate the kinetic friction and the acceleration of the blcok • How much force is needed in order to get it moving? • Fnet = ΣFX • Fnet = FA + Ff • Fnet = 100 N – 44.1 N • Fnet= 55.9 N

  10. SUMMARY • Which letter represents the coefficient of friction? • What are the units for the coefficient of friction? • Where can you find a table for different coefficients of friction? • Describe the two types of friction • List two factors that affect friction

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