Work, and energy

With this foundation, we can now move on to a review of thermodynamics proper, in its origins the transformation of heat into work (and vice-versa), but more broadly taken to mean transformations between forms of energy. So, what is energy and how did the concept originate  

21 If you are interested in the history of this subject one cannot do better than read Maxwell s Demon, 

C von Baeyer, Random House, 1998, where we got most of the good stuff m what follows. 

32 Actually, converting chemical energy stored as bonds to other forms during the metabolism of food. 

FIGURE 10-4 Lavoisier with bis wife (reproduced with the kind permission of the London Science 

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Each physical quantity is expressed in one and only one unit, eg, the meter for length, the kilogram for mass, and the second for time. Derived units are defined by simple equations relating two or more base units. Some are given special names, such as newton for force and joule for work and energy. 

A scalar is a tensor of order zero and has 3° = 1 component. Because it has only magnitude and not direction, no transformation relations are needed. Examples of scalars include speed (but not velocity), work, and energy. 

Joule—The S.I. unit for work and energy. It is equal to the work done by raising a mass of one newton through a distance of one meter (J = Nm), which corresponds to about 0.7 ft-pound. 

Work and energy can be considered as interchangeable we perform work whenever energy powers a physical process, e.g. to propel a car or raise a spoon to the mouth. The work done on a system increases its energy, so the value of U increases, itself causing A U to be positive). Work done by a system corresponds to a negative value of AU. 

The roots of both chemical thermodynamics and contemporary kinetics both lie in the eighteenth-century ideas of chemical "affinity" and "force," transformed into nineteenth-century conceptions of "work" and "energy." Berthollet identified the fundamental difficulty for eighteenth-century theories of affinity in a critique that applied equally to early-nineteenth-century theories of electrochemical dualism. In "Recherches sur les lois de l affinite" (1799), Berthollet wrote,... 

The word thermodynamics implies a relationship between thermal properties, such as temperature, and the dynamic properties described by classic mechanics. Therefore, we shall consider next the dynamic concepts of work and energy and relate them to the properties of thermodynamic systems. 

Isothermal. The procedure used to calculate the work and energy quantities in an isothermal reversible expansion of a real gas is similar to that used for the ideal gas. 

The operative concept is essentially based on the relationship between work and energy, and accounts for the reversibility of processes in thermodynamic cycles (in relation to the development of thermal engines in the 19th century, or steam age cf Kittel, 1989). 

There is essentially no difference between work and energy. Both are measured in joule (J = 1 N m). An outdated unit is the calorie (1 cal = 4.187 J). Energy is defined as the ability of a system to perform work. There are many different forms of energy—e.g., mechanical, chemical, and radiation energy. 

Creating and Maintaining Order Requires Work and Energy... 

Credit for the first recognizable statement of the principle of conservation of energy (heat plus work) apparently belongs to J. Robert Mayer (Sidebar 3.2), who published such a statement in 1842. Mayer also obtained a (slightly) improved estimate, approximately 3.56 J cal-1, for the mechanical equivalent of heat. Mayer had actually submitted his first paper on the energy-conservation principle two years earlier, but his treatment of the concepts of force, momentum, work, and energy was so confused that the paper was rejected. By 1842, Mayer had sufficiently straightened out his ideas to win publication,... 

Let us now determine the overall heat, work, and energy changes in the reversible Carnot cycle. From (4.4a-d), we can evaluate the net work w as... 

What is the difference between heat and temperature Between work and energy Between kinetic energy and potential energy ... 

Work and energy are very closely related in physics. We ve already defined work. Let s now focus on kinetic energy. Kinetic energy is also called energy of motion because one way to define it is one half the product of mass times the square of the speed. 

Describe the difference and the relationship between work and energy. 

Work has the dimensions of a product of force times a distance. Energy has the same dimensions. The units for work and energy may be chosen from any... 

Some conversion factors for the various units of work and energy are... 

Ibid., p. 143, quoting from P. Ewart, On the Measure of Moving Force , Memoirs ofthe Manchester Literary and Philosophical Society, 2nd series, 2(1813), pp. 105—258. This is certainly an important paper so far as conceptual shifts are concerned, and there are signs that the Watts, father and son, reacted positively to it. (See D. S. L. Cardwell, Some Factors in the Early Development of the Concepts of Power, Work and Energy , The British Journal for the History of Science 3 (1967), pp. 209-224, p. 221.)... 

Cardwell, D. S. L., Some Factors in the Early Development of the Concepts of Power, Work and Energy , The British Journal for the History of Science 3 (1967), pp. 209-224. 

In molecular systems, storage of a certain sequence of nucleotides (amount of stored information Imax) depends mainly on the chemical sta bility of the DNA molecule. The information capacity is determined by the number of certain combinations of nucleotides but not by the number of microstates, including accounting the vibrations of aU of the atoms in the DNA chain. The formation of macroinformation is coupled here with the work and energy consumption in the course of biosynthesis of the DNA molecule. Similarly, the information can be implemented by con suming energy for the processes of the information translation and synthe sis of the protein chain. 

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