Lecture 10

Lecture 10 - Today Physics 231 General University Physics...

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1 Physics 231 General University Physics Spring 2007 Lecture 10 Today ± Normal Force ± Application of Newton’s II Law ² Free Body Diagram ² Examples ² More than one object Normal Force ± The normal force (table on monitor) is the reaction of the force the monitor exerts on the table ± Normal means perpendicular, in this case ± How does the force on the TV from the table `know’ to be exactly equal to the weight of TV? ± Notation N N nf ≡≡ G G G Normal Force ± Normal force from compression ± Demo: compress spring/rubber ball/golf ball ± Demo: Bridge (Weight on Meter Stick) ± Discussion: Sitting on Sofa/Block on Table Direction of Normal Force ± Discussion: Bow and Arrow, Meter Stick ± Discussion: Push Book against Wall ± Normal is perpendicular Application of Newton’s II Law ± Assumption ² Objects can be modeled as point particles ± Include only the external forces action on the object ² Do not include reaction forces 123 ... = net i FF F F F Σ = +++ G GGGG / net aF m = G G

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2 Free-Body Diagram ± Identify all forces acting on the object (not by the object) ± Draw a coordinate system ± Draw the object as a dot at the origin ± Draw vectors for each identified force ± Draw and label the net force Free-Body Diagram: Example ± Skier Pulled Uphill Free-Body Diagram: Example ± An ice block propelled across frozen lake Free-Body Diagram: Example ± An elevator elevates upward Objects in Equilibrium ± If the acceleration of an object that can be modeled as a particle is zero, the object is said to be in equilibrium ± Mathematically, the net force acting on the object is zero 0 0 and 0 xy F FF = == ∑∑ Problem ± In an electricity experiment, a 1g plastic ball is
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Lecture 10 - Today Physics 231 General University Physics...

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