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Unformatted text preview: Spring 2011 PHYS 172: Modern Mechanics Lecture 14 – Energy in Macroscopic System Read 7.10 – 7.12 EXAM 2 is next week Time: 8:00-10:00 pm Wed March 9 Place: Elliott Hall Material: lectures 9-14, respective HWs and recitations Problems: multiple choice, 14 questions (70 points) write-up part, hand graded (30 points) Note: no lecture on March 10 ! Energy dissipation E universe = const Energy dissipation: “loss” of energy into forms less useful to us Example: air resistance : Free fall of metal ball Free fall of Paper h t 0.03 s 0.06 s 0.09 s 0 s 1 m 3 Terminal speed mg & air F & dp dt = & & v const = ¡¡¡¡¡ & & terminal speed Mechanism of air resistance Simple model: In average, molecules hit object with larger relative momentum from below than from above, the difference is larger for higher speeds. Too simple! Need to take into account macroscopic “wind”-like phenomenon Fluid dynamics: mathematically complex, beyond the scope of this course Factors determining air resistance...
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This note was uploaded on 04/23/2011 for the course PHYS 172 taught by Professor ? during the Spring '08 term at Purdue University.
- Spring '08