576 Heat and the First Law of ThermodynamicsQ20.9The large amount of energy stored in concrete during the day as the sun falls on it is released atnight, resulting in an higher average evening temperature than the countryside. The cool air in thesurrounding countryside exerts a buoyant force on the warmer air in the city, pushing it upwardand moving into the city in the process. Thus, evening breezes tend to blow from country to city.Q20.10If the system is isolated, no energy enters or leaves the system by heat, work, or other transferprocesses. Within the system energy can change from one form to another, but since energy isconserved these transformations cannot affect the total amount of energy. The total energy isconstant.Q20.11(a) and (b) both increase by minuscule amounts.Q20.12The steam locomotive engine is a perfect example of turning internal energy into mechanicalenergy. Liquid water is heated past the point of vaporization. Through a controlled mechanicalprocess, the expanding water vapor is allowed to push a piston. The translational kinetic energy of
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