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Forces Related to Friction

Forces Related to Friction. F f = µ • F n µ = F f / F n µ is the coefficient of friction. F a = Applied force. F f = force of friction. F n. F g =Weight. dragging a box across the floor. Friction is a force. Opposes motion

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Forces Related to Friction

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  1. Forces Related to Friction Ff = µ • Fn µ= Ff / Fn µ is the coefficient of friction Fa = Applied force Ff =force of friction Fn Fg =Weight dragging a box across the floor

  2. Friction is a force • Opposes motion • depends on the smoothness of the object and the surface it is moving on • depends on the weight of the object • Force of friction = µ x normal force • µ is coefficient of friction • related to smoothness • 0.1 for ice, 0.2 for smooth, 0.5 for rough surface

  3. Measuring force of friction • When block moves at constant velocity, the force of friction equals the applied force • The force of friction opposes the applied force • If the surface is flat, the normal force equals the weight. • The force of static friction is usually slightly larger than the force of sliding friction.

  4. Static and Kinetic Friction • Static Friction force happens when surfaces do not slip past each other • walking on the floor • pushing on a book before it moves • Kinetic friction happens when surfaces slide • sliding in stockings on waxed floor • pushing a book moving on the desk • Force of static friction keeps increasing until the object moves • Force of static friction is greater than Force of kinetic friction • Static and Kinetic friction obey the same laws • static is greater than kinetic

  5. Static and Kinetic Friction • Kinetic Friction • Object is moving • Surfaces are sliding passed each other • Static Friction • Objects not moving • Static Friction balances force of the push

  6. Static and Kinetic FrictionABS Brakes

  7. Unbelievable Friction Facts • Force of friction does not depend on area • thin block and wide block have same Ff • Force of friction increases with weight • Coefficient of friction is independent of weight •  does not depend on weight •  does not depend on area •  depends only on the two surfaces

  8. Ramp at an angle • The normal force is less than the weight • A part of the weight opposes the frictional force (down ramp) • As the angle gets larger, normal force decreases and part of weight down ramp increases.

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