Force of Friction.

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Presentation transcript:

Force of Friction

Force of friction (Ff) is given by the equation Friction is created whenever two surfaces try to move past one another. On the microscopic level, irregularities in each surface impede motion, therefore the smoother the surface the less friction. Force of friction (Ff) is given by the equation Where: FN = the normal (supporting) force μ = coefficient of friction = greater for rougher surfaces Ff = µFN

Frictionstatic > Frictionkinetic There are 2 types of friction: Static Friction: friction on a motionless body Kinetic Friction: friction on a moving body Note that the irregularities in a static object will tend to “dig in” more and generally: Frictionstatic > Frictionkinetic μs > μk

Ex 1: A 3.75 kg block is pushed along a tabletop with a force of 45.0N. The coefficient of friction is 0.65. a) Find the force of friction. b) Find its acceleration.

Ex 2: A 0.200 kg puck is pushed along a sheet of ice with a force of 0.240 N. If it moves at a constant velocity, find the coefficient of friction.

Ex 3: A 1.12 kg textbook is pushed horizontally against a wall with a coefficient of friction of 0.465. What is the least amount of force required to keep the book from slipping?

Ex 4: A 24 kg box is suspended by a rope from a pulley which leads to another 28 kg box on a 40° incline. The coefficient of friction between the 28 kg box and the ramp is 0.15. Determine the acceleration of the boxes and the tension in the rope.