Lab 106 - Steven Valentin Group Noelle Fifi Marlyn PHYS...

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Steven Valentin Group: Noelle, Fifi, Marlyn PHYS 111A-010 Tao Zhou February 23, 2016 Title: Lab 106(2): Static and Kinetic Frictions Introduction : The objectives of this lab is to understand the coefficients of static friction and kinetic friction by measuring the frictions between surfaces, analyzing these forces using free- body diagrams, and experimentally test our predictions by pulling a cart along an inclined plane and observing the friction involved. Theory: When a body is at rest on a surface, it experiences both a gravitational force (F g ) and a normal force (F N ). When a force is applied to that body (F app ) in a horizontal direction, a frictional force (f) balancing the applied forced is directed in the opposite direction and is called the static frictional force (fs). When the applied force moves the container free from the static frictional force, the maximum static friction (fs, max) has been surpassed and the body now slides in the horizontal direction of the applied force. An applied force must continue to act on the body in order to keep it moving, however this force doesn’t have to be as great as the force required to break it free from the maximum static friction. As the body moves, it experiences kinetic frictional force (f k ) in the opposite direction of the applied force. The relationships between the frictional forces and the normal forces are: fs, max = μ s FN, where μ s is a constant called the coefficient of static friction. f k = μ k FN, where μ k is a constant called the coefficient of kinetic friction. Both friction coefficients depend only on the nature of the two surfaces in

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