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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 45 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.]:lNm = 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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 Fall '11
 Staff
 Dynamics

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