4.2 Gravity, Normal Force, and Friction

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Gravity and Weight

GRAVITY AND WEIGHT
Universal
Gravity 		Fg = Gm1m2 / r2            G=6.67×10-11 N•m2 / kg2
Weight W = mg      (for an object near the surface of the Earth)
For an object on the surface of the earth,
Fg = G mME / rE2 = mg     so     g = G ME / rE2 = 9.8 m/s2

Normal Force and Friction

NORMAL FORCE AND FRICTION
Normal Force Perpendicular component of the contact force that a surface exerts on an object.
Static Friction Ff max = µsFN
µs = coefficient of static friction
Kinetic Friction Ff = µkFN
µk = coefficient of kinetic friction