1. UNIT 4 Forces and the Laws of Motion

2. ConcepTest 5.1aGravity and Weight I ConcepTest 5.1a Gravity and Weight I 1) F g is greater on the feather 2) F g is greater on the stone 3) F g is zero on both due to vacuum 4) F g is equal on both always 5) F g is zero on both always What can you say about the force of gravity F g acting on a stone and a feather?

3. The force of gravity (weight) depends on the mass of the object!! The stone has more mass, therefore more weight. ConcepTest 5.1aGravity and Weight I ConcepTest 5.1a Gravity and Weight I 1) F g is greater on the feather 2) F g is greater on the stone 3) F g is zero on both due to vacuum 4) F g is equal on both always 5) F g is zero on both always What can you say about the force of gravity F g acting on a stone and a feather?

4. Force of Static Friction FaFa F fs m F g = mg FNFN Everyday Forces

5. Force of Kinetic Friction FaFa F fk m F g = mg vivi FNFN Everyday Forces

6. Steel on steel 0.74 0.57 Aluminum on steel 0.61 0.47 Copper on steel 0.53 0.36 Rubber on concrete 1.0 0.8 Wood on wood 0.25-0.5 0.2 Glass on glass 0.94 0.4 Waxed wood on wet snow 0.14 0.1 Waxed wood on dry snow ------ 0.04 Metal on metal (lubricated) 0.15 0.06 Ice on ice 0.1 0.03 Teflon on Teflon 0.04 0.04 Coefficients of Friction μsμs μkμk Everyday Forces

7.   x y    mg mg cos(  ) mg sin(  ) Review of Similar Triangles Everyday Forces

8.   FNFN mg sin(  ) mg mg cos(  ) Find the acceleration on a smooth incline (NO friction) Σ F y = 0 F N = mg cos(θ) Σ F x = ma Everyday Forces a mgsin(  ) = ma a = gsin(  ) mg sin(  ) y x

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