The laws of thermodynamics are time-honored principles that describe the behavior of energy. (2) These laws are based on certain observations about the behavior of matter and energy that are remarkably invariable from one instance to the next. (3) Such consistency leads to predictions. (4) What happens, for example, to objects raised above the ground and then released? (5) What happens to an object that is heated and then set aside, away from the heat? (6) Everyone can predict that the first object will fall to the ground and that the second will cool. (7) Such observations, made time and again, have eventually led to the formulation of laws of nature. The First Law (8) The first law of thermodynamics states that energy can neither be created nor destroyed, but it can be converted from one form to another. (9) Understandably, the first law is also called the law of conservation of energy. (10) What the first law means is that the total amount of energy present in a system remains constant. (11) The concept refers to idealized conditions that exist only in what is called an "isolated system" one in which matter and energy cannot enter and leave. (12) Such systems do not really exist (except perhaps as the universe itself) but are contrived as models by scientists who wish to test their ideas under hypothetical conditions that can be limited and controlled. Energy Transitions: A Case History (13) Energy changes occur in a variety of ways. (14) When you start your lawnmower engine, you can begin to appreciate the idea of energy conservation. (15) Consider that the gasoline in the lawnmower's tank is a veritable storehouse of chemical energy, locked away in the chemical bonds that hold the carbon and hydrogen of the gasoline molecules together. (16) As you pull the cord, a mix of gasoline vapor and air encounters an electrical discharge from the spark plug, and the engine starts. (17) Chemical energy in the fuel molecules becomes heat energy, and heat then expands the gases in the engine cylinder. (18) The next energy transformation is to mechanical energy, or energy of motion, which comes about when the expanding gases push against the piston. (19) The piston moves up and down, its connecting rod rotating the crankshaft, which spins the lawnmower blade. (20) At certain points in the piston's movement, valves open, and the expanding gases escape into the surroundings, their energy dissipating as heat. (21) The escaping gases-carbon dioxide and water vapor-are at a considerably lower energy level than gasoline, and the difference between the two energy levels is to be found in exhausted heat and the energy of motion. (22) The latter largely becomes heat as well, as the moving parts of the lawnmower encounter friction. (23) What we see here is characteristic of energy as it changes form. (24) Energy transformations are accompanied by the formation of heat, and when such heat has dissipated, it is no longer capable of work, at least as far as that system (in this case, the lawnmower) is concerned. (25) The transition of systems with great energy to systems with low energy extends beyond lawnmowers; it is a tendency of the universe at large. (26) Physicists express this general observation in the second law of thermodynamics. The Second Law (27) The second law of thermodynamics tells us that energy transitions are imperfect-that some energy is always lost, usually as heat, in each transition. (28) Again, in the transitions from the chemical bond energy in gasoline to the mechanical energy in the spinning lawnmower blade, much of the original energy is lost as heat. (29) The energy is not lost from the system; it is just that such heat energy is normally not available to do useful work. Question9. What clues are there to help you find the most important information in this passage? a. Title b. Sentence 1 c. Subtitles d. Italics e. All of the above