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ENERGY   TRANSFORMATIONS
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Another  principle,  the  PRINCIPLE  OF  THE CONSERVATION   OF   MATTER,   states   that matter can be neither created nor destroyed, but only  transformed.  As  you  probably  know,  the development  of  the  atom  bomb  demonstrated  that matter   can   be   converted   into   energy;   other developments  have  demonstrated  that  energy  can be converted into matter. Therefore, the principle of  the  conservation  of  energy  and  the  principle of  the  conservation  of  matter  are  no  longer considered as two parts of a single law or principle but  are  combined  into  one  principle.  That principle  states  that  matter  and  energy  are interchangeable, and the total amount of energy and matter in the universe is constant. The interchangeability of matter and energy is  mentioned  here  only  to  point  out  that  the statement energy in must equal energy out is not strictly true for certain situations. However, any noticeable  conversion  of  matter  into  energy  or energy  into  matter  can  occur  only  under  very special  conditions,  which  we  need  not  consider now. All the energy transformations that we will deal  with  can  be  understood  quite  simply  if  we consider only the principle of the conservation of energy—that   is, ENERGY   IN   EQUALS ENERGY  OUT. Transformation of Heat to Work (Laws of Gases) The energy transformation from heat to work is the major interest in the shipboard engineer- ing plant. To see how this transformation occurs, we  need  to  consider  the  pressure,  temperature, and  volume  relationships  that  hold  true  for  gases. Robert  Boyle,  an  English  scientist,  was  among the first to study the compressibility of gases. In the  middle  of  the  17th  century,  he  called  it  the “springiness” of air. He discovered that when the temperature of an enclosed sample of gas was kept constant  and  the  pressure  doubled,  the  volume was  reduced  to  half  the  former  value.  As  the applied  pressure  was  decreased,  the  resulting volume  increased.  From  these  observations  he concluded  that  for  a  constant  temperature,  the product  of  the  volume  and  pressure  of  an  enclosed gas  remains  constant.  This  conclusion  became Boyle’s  law. You can demonstrate Boyle’s law by confining a quantity of gas in a cylinder that has a tightly fitted   piston.   Apply   force   to   the   piston   to compress the gas in the cylinder to some specific volume.  If  you  double  the  force  applied  to  the Figure 2-5.—Compressibility of gas. piston,  the  gas  will  compress  to  one  half  its original  volume  (fig.  2-5). Changes in the pressure of a gas also affect the density. As the pressure increases, its volume decreases;   however,   no   change   occurs   in   the weight of the gas. Therefore, the weight per unit volume  (density)  increases.  So,  the  density  of  a gas  varies  directly  as  the  pressure  if  the temperature is constant. In  1787,  Jacques  Charles,  a  Frenchman, proved  that  all  gases  expand  the  same  amount when  heated  1  degree  if  the  pressure  is  kept constant.  The  relationships  that  these  two  men discovered  are  summarized  as  follows: l Boyle’s law—when the temperature is held constant,  an  increase  in  the  pressure  on  a  gas causes   a   proportional   decrease   in   volume.   A decrease  in  the  pressure  causes  a  proportional increase in volume, as shown in figure 2-6. At sea level,  the  balloon  has  a  given  volume  with  respect to temperature and atmospheric pressure. As the balloon  descends  1  mile  below  sea  level,  the volume of the balloon decreases due to increased atmospheric pressure. Conversely, as the balloon ascends  to  1  mile  above  sea  level,  the  balloon expands as the atmospheric pressure decreases. l Charles’s law—when the pressure is held constant, an increase in the temperature of a gas causes   a   proportional   increase   in   volume.   A decrease  in  the  temperature  causes  a  proportional decrease   in   volume,   as   shown   in   figure   2-7. Balloons A and B have an outside pressure of 10 pounds  per  square  inch  (psi).  Both  have  the  same volume of air. Balloon A is at 40°F and balloon B   is   at   100°F.   This   shows   that   increased temperature causes the balloon size to increase. 2-10






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