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# Lect_13 - Motivation to go beyond Newton's laws Newton...

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Lecture 13 Work and the Work/Kinetic Energy Theorem Motivation to go beyond Newton ’s laws s laws Loop the loop R mg N The normal force has different direction and magnitude at every point on the track!! Writing and solving Newton’s laws can be a nasty experience… (see appendix of lecture 15) 22 net, 11 x i f F mv ∆= Playing around with Newton Playing around with Newton ’s 2nd law. s 2nd law. WORK ( W ) done by force over displacement Consider the motion of a bead of mass m on a straight wire pushed by a constant net force x parallel to the wire, along a displacement : net,x xx Fma = Force produces acceleration: ∆= − 2 axv v v i f Acceleration produces change in speed: 2 xv v Change in KINETIC ENERGY ( K ) of the bead This is an expression of the “effectiveness” of the force. net WK =∆ Of how a force applied over a distance… …changes something in the system Work The “external agent” that changes the amount of kinetic energy (the state) in the system W Fx = Kinetic energy The “internal” quantity (state) of the system 2 1 2 Km = net, Work/Kinetic Energy Theorem

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m x Initial kinetic energy K i Final kinetic energy f > i Positive work W > 0 Energy source Work is energy being transferred F net,x Units for work and energy: SI: Not to be confused with: Calorie (or food calorie) 1 Cal = 1000 cal calorie 1 cal = 4.184 J Kilowatt-hour KWh Other common units: Joule 1 J = 1 N · m Energy Many types of energy: kinetic energy electric energy internal –thermal- energy elastic energy chemical energy •E t c . Energy is transferred and transformed from one type to another and is never destroyed or created.
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Lect_13 - Motivation to go beyond Newton's laws Newton...

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