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Friction

Friction. Frictional Forces. Friction has its basis in surfaces that are not completely smooth:. Static Friction. Static Friction. Static friction keeps an object from starting to move when a force is applied.

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Friction

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  1. Friction

  2. Frictional Forces Friction has its basis in surfaces that are not completely smooth:

  3. Static Friction

  4. Static Friction • Static friction keeps an object from starting to move when a force is applied. • Static frictional force has a maximum value, but may take on any value from zero to the maximum,

  5. Static Frictional Forces (6-2) where (6-3)

  6. Kinetic Friction Fpush > fk = mkn

  7. Kinetic Friction Kinetic friction: the friction experienced by surfaces sliding against one another Kinetic frictional force depends on the normal force: (6-1) Constant is called the coefficient of kinetic friction.

  8. Kinetic Friction and Speed kinetic friction is independent of relative speed of the surfaces, and of their area of contact.

  9. Coefficients of Friction fs£ msFn fs max = msFn fk = mkFn Typically, ms>mk

  10. Horizontal Retarding Friction A cruise-ship passenger uses a shuffleboard cue to push a shuffleboard disk of mass 0.40 kg horizontally along the deck, so that the disk leaves the cue at a speed of 8.5 m/s. The disk then slides a distance of 8.0 m. What is the coefficient of kinetic friction between the disk and deck? m = 0.40 kg v0x = 8.5 m/s x0 = 0 x = 8.0 m vx = 0 0 0

  11. Friction ACT1 You push two identical bricks across a tabletop with constant speed v. Which Case, as shown above, requires more force Fn? a. F1>F2 b. F1=F2 c. F1<F2d.Need to know brick areas to answer

  12. Inclined Plane Friction Suppose a 20 kg object is sliding down a 50o inclined plane. If µk = 0.4 between the plane surface and the object, what is the object’s acceleration down the plane? How long will it take the object to slide 5.0 m if it starts from rest?. k F

  13. Friction with  Component of Tension Two children sitting on a sled at rest in thesnow ask you to pull them. You oblige by pullingon the sled’s rope, which makes an angle of 40°with the horizontal. The children have acombined mass of 45 kg, and the sled has amass of 5.0 kg. The coefficient of kinetic friction is mk=0.15. Find the acceleration of the sled and children if the rope tension is 140 N.

  14. Antilock Brakes

  15. Antilock Brakes A car is traveling at 30 m/s along a horizontal road. The coefficients of friction are ms=0.50 and mk=0.40. (a) What is the braking distance Dxa with antilock brakes? (b) What is the braking distance Dxb if the brakes lock?

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