Chapter 7

# Chapter 7 - Announcement Exam #1 grades are posted on...

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Announcement Exam #1 grades are posted on E-learning Exam #1 average is 8.8 out of 12 (73.3%) Master copy of exam #1 (correct answer 1) on E-learning

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Exam #1 Statistics 0 0 : : 0 1 : : 1 2 :** :** 1 3 :** :** 6 4 :************ :************ 4 5 :******** :******** 3 6 :****** :****** 9 7 :****************** :****************** 12 8 :************************ :************************ 10 9 :******************** :******************** 12 10 :************************ :************************ 15 11 :****************************** :****************************** 13 12 :************************** :**************************
Chapter 7 Work Kinetic Energy HITT quiz Work done by gravitational force

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Energy and Work: loose definitions Very common terms, beware: everyday life meanings are not identical what these terms mean in physics Loose definitions in physics: • A moving body is said to have kinetic energy ; the faster the object moves, the more energy it has. • Something capable of increasing kinetic energy of an object is said to have potential energy stored. • In order to increase object’s kinetic energy, one needs to apply a force and do some work .
Work Force · Time = ? Force · Distance = ? Both are actually very much relevant: • F · t characterizes the change in momentum (to be discussed later) • F · d characterizes the change in energy, i.e. For a constant force F acting over a displacement d θ cos Fd d F W = = r r

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Units Work = Energy: Joule (J) Power: Watt (W) 1 horsepower = 746 Watt Energy = Power x time: 1 kWatt-hour = 3.6 MJ 2 2 kg m 1 J = s 2 3 J kg m 1 W = = s s W arning! Do not confuse W ork, W att, W eight
Why do we tell you to memorize this? a) Lot of mechanical problems can’t be solved exactly but we still want to understand part of the problem. b) Because these concepts help understand complex mechanical systems. You can understand why by studying the history a little First, some questions about billiards http://www.youtube.com/watch?v=p_aOWYYnIHo http://comp.uark.edu/~jgeabana/mol_dyn/KinThI.html

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What did you see? There are many physical systems with many particles where velocities change a lot. Gottfried Wilhelm Leibnitz (Newton’s competitor) ~ 1680: Sometimes even when velocities change, something stays the same: Total kinetic energy of all the particles didn’t change in gas simulation: 2 1 1 2 N i i i K m v = =
Statement about a physical quantity which doesn’t change with time. Energy, momentum…

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## This note was uploaded on 03/12/2010 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.

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Chapter 7 - Announcement Exam #1 grades are posted on...

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