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			'''Thermodynamics''' is gay.
	'''Thermodynamics''' (from the ] ''thermos'' meaning heat and ''dynamis'' meaning power) is a branch of ] that studies the effects of temperature, pressure, and volume changes on ]s at the ] scale. In simpler terms, heat means ‘energy in transit’ and dynamics relates to ‘movement’. Thus, in essence thermodynamics studies how energy instills movement.

	The starting point for most thermodynamic considerations are the ]. These laws postulate that ] can be exchanged between physical systems in the form of ] and ], as well as the existence of a quantity named ], which can be associated with every system.

	From its inception, thermodynamics developed out of the need to increase the ] of early ]. The first engine constructed was the 1698 Savery engine as shown below:
	]]

	== Overview ==
	Thermodynamics in most regards is held to be a difficult subject. In ] for example, which teaches one of the more rigorous variations of such, thermodynamics is considered a weeder course. One of the better ways to learn thermodynamics is to follow a ground up development of its concepts and principles, beginning with ] as SI and English, ] as pressure, temperature, and volume, etc., properties of substances as gas, vapor, liquid, and solid, etc., ], the laws of thermodynamics, ], continuing onward through such advanced subjects as multi-phase reaction thermodynamics, high-speed gas flow thermodynamics, or molecular thermodynamics, etc.

	A difficult concept in thermodynamics is that of "]". In particular, the entropy of a system exchanging no ] with the outside can never decrease with ]. As such, entropy allows predictions on the transformations and energy exchanges that are accessible to a given system. Related to entropy, ] or ] is one of the underlying theories that sustain thermodynamics; it provides a way to predict the entropy of a thermodynamic system, based on the ] analysis of the fluctuations the system experiences over a set of ]s

	== History ==
	{{main\|History of thermodynamics}}
	]
	A short history of thermodynamics begins with the British physicist and chemist ] who in 1656, in coordination with English scientist ], invented the air pump. Using this pump, Boyle and Hooke noticed the pressure-temperature-volume correlation. In time, the ] was formulated. Soon thereafter, in 1679, based on these concepts, an associate of Boyle's named ] built a bone digester, which is a closed vessel with a tightly fitting lid that confines steam until a high pressure is generated.

	Later designs implemented a steam release valve to keep the machine from exploding. By watching the valve rhythmically move up and down, Papin conceived of the idea of a piston and cylinder engine. He did not however follow through with his design. Nevertheless, in 1698, based on Papin’s designs, engineer ] built the first engine. These early engines being crude and inefficient attracted the attention of the leading scientists of the time. One such scientist was ], the “father of thermodynamics”, who in 1824 published ''“Reflections on the Motive Power of Fire”,'' a discourse on heat, power, and engine efficiency. This marks the start of thermodynamics as a modern science.
	<br style="clear:both;" />

	== Thermodynamic systems ==
	{{main\|System (thermodynamics)}}

	Of most importance in thermodynamics is the concept of the “system”. A system is the region of the universe under study. A system is separated from the remainder of the universe by a boundary which may be imaginary or not, but which, by convention delimits a finite volume. The possible exchanges of ], ], or ] between the system and the surroundings take place across this boundary. There are four dominate classes of systems:
	]
	#''Isolated Systems'' – matter and energy may not cross the boundary.
	#''Adiabatic Systems'' – heat and matter may not cross the boundary.
	#''Closed Systems'' – matter may not cross the boundary.
	#''Open Systems'' – heat, work, and matter may cross the boundary.

	For closed systems, as time goes by, internal differences in the system tend to even out; pressures and temperatures tend to equalize, as do density differences. A system in which all equalizing processes have gone practically to completion, is considered to be in a ] of ].

	In thermodynamic equilibrium, a system's properties are, by definition, unchanging in time. Systems in equilibrium are much simpler and easier to understand than systems which are not in equilibrium. Often, when analyzing a thermodynamic process, it can be assumed that each intermediate state in the process is at equilibrium. This will also considerably simplify the situation. Thermodynamic processes which develop so slowly as to allow each intermediate step to be an equilibrium state are said to be ] processes.

	== Thermodynamic parameters ==
	{{main\|Conjugate variables (thermodynamics)}}

	The central concept of thermodynamics is that of ], the ability to do ]. As stipulated by the ], the total energy of the system and its surroundings is conserved. It may be transferred into a body by heating, compression, or addition of matter, and extracted from a body either by expansion, cooling, or extraction of matter. Just as in ], energy transfer is effected by a force causing a displacement, with the product of the two being the amount of energy transferred. In a similar way, thermodynamic systems can be thought of as transferring energy as the result of a generalized force causing a generalized displacement, with the product of the two being the amount of energy transferred. These thermodynamic force-displacement pairs are known as ]. The most common conjugate thermodynamic variables are pressure-volume (mechanical parameters), temperature-entropy (thermal parameters), and chemical potential-particle number (material parameters).

	== Thermodynamic instruments ==
	{{main\|Thermodynamic instruments}}

	There are two types of thermodynamic instruments, the '''meter''' and the '''reservoir'''. A thermodynamic meter is any device which measures any parameter of a ]. In some cases, the thermodynamic parameter is actually defined in terms of an idealized measuring instrument. For example, the ] states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This principle, as noted by ] in 1872, asserts that it is possible to measure temperature. An idealized ] is a sample of an ideal gas at constant pressure. From the ] ''PV=nRT'', the volume of such a sample can be used as an indicator of temperature; in this manner it defines temperature. Although pressure is defined mechanically, a pressure-measuring device, called a ] may also be constructed from a sample of an ideal gas held at a constant temperature. A ] is a device which is used to measure and define the internal energy of a system.

	A thermodynamic reservoir is a system which is so large that it does not appreciably alter its state parameters when brought into contact with the test system. It is used to impose a particular value of a state parameter upon the system. For example, a pressure reservoir is a system at a particular pressure, which imposes that pressure upon any test system that it is mechanically connected to. The earths atmosphere is often used as a pressure reservoir.

	== Thermodynamic states ==
	{{main\|Thermodynamic state}}

	When a system is at equilibrium under a given set of conditions, it is said to be in a definite ''state''. The state of the system can be described by a number of ]s and ]s. The properties of the system can be described by an ] which specifies the relationship between these variables. State may be thought of as the instantaneous quantitative description of a system with a set number of variables held constant.

	== Thermodynamic processes ==
	{{main\|Thermodynamic processes}}

	A '''thermodynamic process''' may be defined as the energetic evolution of a thermodynamic system proceeding from an initial state to a final state. Typically, each thermodynamic process is distinguished from other processes, in energetic character, according to what parameters, as temperature, pressure, or volume, etc., are held fixed. Furthermore, it is useful to group these processes into pairs, in which each variable held constant is one member of a ] pair. The five most common thermodynamic processes are shown below:

	#An ] occurs at constant pressure.
	#An ] occurs at constant volume.
	#An ] occurs at a constant temperature.
	#An ] occurs at a constant entropy.
	#An ] occurs without loss or gain of heat.

	== The laws of thermodynamics ==
	{{main\|Laws of thermodynamics}}

	In thermodynamics, there are four laws of very general validity, and as such they do not depend on the details of the interactions or the systems being studied. Hence, they can be applied to systems about which one knows nothing other than the balance of energy and matter transfer. Examples of this include ]'s prediction of ] around the turn of the ] and current research into the thermodynamics of ]s.

	The four laws are:

	* ], about the ] of ]
	**If systems A and B are in thermal equilibrium, and systems B and C are in thermal equilibrium, then A and C are also in thermal equilibrium.
	**Two systems in thermal equilibrium with a third system, all must be in equilibrium with each other.
	* ], or a statement about the ]
	**The work exchanged in an adiabatic process depends only on the initial and the final state and not on the details of the process.
	**The heat energy flowing into a system is equal to the sum of the increase in the internal energy of the system and the work done by the system.
	**The change in internal energy of a system is <math>\Delta</math>U = q + w, where q is heat flow and w is work.
	* ], about ]
	**The ] of an isolated system never decreases (see ])
	**A system operating in contact with a thermal reservoir cannot produce positive work in its surroundings (])
	**A system operating in a cycle cannot produce a positive heat flow from a colder body to a hotter body (])
	* ], about ] ]
	**All processes cease as temperature approaches zero.
	**As temperature goes to 0, the entropy of a system approaches a constant

	== Thermodynamic potentials ==
	{{main\|Thermodynamic potentials}}

	As derived from the energy balance equation on a thermodynamic system there exist energetic quantities called ], being the quantitative measure of the stored energy in the system. The four most well known potentials are:

	{\| border="0" cellpadding="4" style="margin: 0 0 1em 1em"
	\|-
	\|]
	\|<math>U\,</math>
	\|-
	\|]
	\|<math>A=U-TS\,</math>
	\|-
	\|]
	\|<math>H=U+PV\,</math>
	\|-
	\|]
	\|<math>G=U+PV-TS\,</math>
	\|}

	Potentials are used to measure energy changes in systems as they evolve from an initial state to a final state. The potential used depends on the constraints of the system, such as constant temperature or pressure. Internal energy is the internal energy of the system, enthalpy is the internal energy of the system plus the energy related to pressure-volume work, and Helmholtz and Gibbs free energy are the energies available in a system to do useful work when the temperature and volume or the pressure and temperature are fixed, respectively.

	== Thermodynamic evolution ==
	{{main\|Thermodynamic evolution}}

	In 1875 Austrian physicist ] declared: ''"the general struggle for existence of animate beings is a struggle for ]"''. Ever since, there has been a continuous search to elucidate the thermodynamic mechanism behind evolution. As it is generally agreed that life evolved from non-life, a process called ], by some form of ], and as it is understood that both life and non-life abide by the ], then, in theory, it is reasoned that there should exist a functionable model of thermodynamic evolution. This line of research defines the field of thermodynamic evolution.

	== Quotes & humor ==
	{{main\|Quotes & humor (thermodynamics)}}

	* A common scientific joke expresses the three laws simply and surprisingly accurately as:

	: '''Zeroth:''' ''"You must play the game."''
	: '''First:''' ''"You can't win."''
	: '''Second:''' ''"You can't break even."''
	: '''Third:''' ''"You can't quit the game."''

	== See also ==
	* ]
	* ]
	* ] - sometimes called the ''Fourth Law of Thermodynamics''
	* ]
	* ]
	* ]
	* ]
	=== Related lists and timelines ===
	* ]
	* ]
	* ]
	=== Related fields ===
	* ]
	* ]
	* ]
	* ]
	* ] (also known as chemical thermodynamics)
	* ]
	* ]
	* ]
	* ]
	=== Wikibooks ===
	*
	== References ==
	* {{Book reference \| Author=Perrot, Pierre \| Title=A to Z of Thermodynamics \| Publisher=Oxford University Press \| Year=1998 \| ID=ISBN 0198565526}}
	* {{Book reference \| Author=Kroemer, Herbert; Kittel, Charles \| Title=Thermal Physics \| Publisher=W. H. Freeman Company \| Year=1980 \| ID=ISBN 0716710889}}
	* {{Book reference \| Author=Cengel, Yunus A.; Boles, Michael A. \| Title=Thermodynamics - An Engineering Approach \| Publisher=McGraw-Hill \| Year=2005 \| ID=ISBN 0073107689}}
	== External links ==
	*
	*
	*
	=== Laws ===
	*
	*
	*
	*
	*

	{{Physics-footer}}

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Revision as of 03:49, 15 December 2005

Thermodynamics is gay.