13-2 Internal energy(p]ae) in a system of particles 1 Consider an ice skater she starts at rest and then extend her arm to push herself away from the ailing at the edge of a skating rink(溜冰场) + Use work-energy railing relationship to analyze g △+△U=Wgxr F The system chosen Ice only include the skater g →△U=0 Ch 13 Energy III: Conservation of energyCh.13 Energy III: Conservation of energy 13-2 Internal energy (内能) in a system of particles 1. Consider an ice skater. She starts at rest and then extend her arm to push herself away from the railing at the edge of a skating rink（溜冰场）. •••• ice railin g Use work-energy relationship to analyze: K + U =Wext The system chosen only include the skater Mg N F U = 0