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ch4sec4 - Weight Fg=mag ag = 9.81 m/s2 Comparing Mass and...

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Weight F g =ma g a g = 9.81 m/s 2
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Comparing Mass and Weight
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Normal Force The normal force acts on a surface in a direction perpendicular to the surface. F g F f F a F n y x θ F g,x F g,y , x a f g x F F F F Σ = - + + x ma = , y n g y F F F Σ = - y ma = 0 = , n g y F F =
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Normal Force
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Friction
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The quantity that expresses the dependence of frictional forces on the particular surfaces in contact is called the coefficient of friction, μ . The Coefficient of Friction f n F F μ = f n F F μ =
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Coefficients of Friction You will find this table in your text
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Coefficients of Friction k k n F F μ = ,max S s n F F μ = Coefficient of static friction : k k n F F μ = ,max S n s F F μ = Coefficient of kinetic friction :
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In free-body diagrams, the force of friction is always parallel to the surface of contact. The force of kinetic friction is always opposite the direction of motion. To determine the direction of the force of static friction, use the principle of equilibrium. For an object in equilibrium, the frictional force must point in the direction that results in a net force of zero. Friction Forces in Free-Body Diagrams g F n F (force of kinetic friction) k F If moving, kinetic friction opposes motion If not moving, static friction is in a direction that provides equilibrium g F n F (force of static friction) S F a F
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Net Force equations from Free Body Diagrams (force of gravity) g F (force of air resistance) r F (force of gravity) g F (normal force) n F (force of friction) f F (applied force = push) a F 0 x F Σ = y r g y F F F ma Σ = - = x a f x F F F ma Σ = - = y n g y F F F ma Σ = - =
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Net Force equations from Free Body Diagrams n F a F g F k F θ n F a F g F k F θ cos x a k x F F F ma θ Σ = - = sin y n a g y F F F F ma θ Σ = + - = cos x a k x F F F ma θ Σ = - = sin y n a g y F F F F ma θ Σ = - - =
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Net Force equations from Free Body Diagrams n F g F k F θ x y a F g F k F θ
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