081811 - Some Objectives 0 Identity the various forms of...

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Unformatted text preview: Some Objectives: 0 Identity the various forms of energy 0 Determine how a. S\-‘stem is altered following energy transfer to / from the system 0 Examine how energy can be transformed from one form to another. Example: A typical human body requires E : 2000 keal - 4.2 k.l/kcal : 8400 kl of energy a day. This amount of energy is approximately equivalent to E fidcla Wit“ W=§ = 100 w . 2/1 hr . 3000 s/hr 3 : 8.04 x 10‘j .J : 8040 RJ 0 The energy required to power a 100 W light bulb for a day: o The energy required to move a typical ear for 1 mile. Assuming that the ear gets 15 mi/gal. and using a density of 0.7 kg / l for gasoline, then the mass of gasoline burned is 1 mi - 0.7 kg/l m = 15 mi/gsl - 0.26 gal/l kosl M "2— 10 .— The heating value 01‘ gasoline is 4-5 X 10'3 lei/kg so 3 W E : 0.170 kg - 4.5 x 103 kJ/kg m 8100 id 0 The energy required to raise the temperature of around 26 gal of water by 200C: E : mCAT : [)VCAT : 1 kg/l - 3.85 l/gal - 26 gal - 4.2 lctl/kgOC - 20°C : 8400 la] o The energy required to raise a 100 kg mass a height of 8571 m: E : mgAz : 100 kg . 9.8 m/s2 . 8571 m : 8.4 x 106 J : 8400 kl o The energy required to accelerate a 100 kg body from rest to a velocity of 410 m/ s: E = émv2 1 9 = 5‘ 100 kg ‘ {410 III/s}' : 8.4 x 106 .1 = 8400 kl These are all forms of energy. They all have the same unit of measure (i.e., ._J or kl). However, they are not entirely equivalent. Most of us would not be able to climb 8571 m on the energy provi<’led solely by the 2000 keal. It would also be 277712055in6 to use the N 8400 kJ of ‘heat7 released . r a 4 , from burmng the gas to power an englne that would hit the 100 kg mass this distance. 00 1/: t®<s crooks were 8% 3 ”2 ~% in assay?” On the other hand7 we could devise a way in which we too ' the energy obtained from dropping the 100 kg weight a ('listanee 01'8571 m, and use it to heat the 26 gal of water by 200C. .‘ < Vl- hat is energy? 1.]:lN-m = work required to displace a force of 1 N over a displacement of 1 Hi. \Vork: a form of energy. W’e i‘lJl derive a simple relation between work and the energy of 2 system Sailor. Fog—M in Law tkwéamc 4~J3s515 4fflmé. and w : gm (V3 — V12) + mg (mg 7 m1) VJ =AKE+APE H7 = AKE + APE This result illustrates some key points: 0 There are three forms of energy appearing in the formula: work1 kinetic energy, and potential energy. 0 Work is a 'orm of energy that is transferred to (or from) a system c [{E and P3 are forms of energy that Characterize the energy of a system (i.e., energy contained in a system). 0 The formula is in the form of a (:onseruat'llrm law: energy translerrew to a system : energy change of system, W7 = AKE + APE The formula is a rudimentary form of the F Mast Law of thermodynamics. We will want to make this law more general. In particular, we will need to 0 Account for additional means of energy transfer (heat) I Account for additional means of energy storage (soiealled internal energy) ...
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