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* [[Work (physics)|Work]] is a process of transferring energy to or from a system in ways that can be described by macroscopic mechanical forces exerted by factors in the surroundings, outside the system. Examples are an externally driven shaft agitating a stirrer within the system, or an externally imposed electric field that polarizes the material of the system, or a piston that compresses the system. Unless otherwise stated, it is customary to treat work as occurring without its [[dissipation]] to the surroundings. Practically speaking, in all natural process, some of the work is dissipated by internal friction or viscosity. The work done by the system can come from its overall kinetic energy, from its overall potential energy, or from its internal energy.

* [[Work (physics)|Work]] is a process of transferring energy to or from a system in ways that can be described by macroscopic mechanical forces exerted by factors in the surroundings, outside the system. Examples are an externally driven shaft agitating a stirrer within the system, or an externally imposed electric field that polarizes the material of the system, or a piston that compresses the system. Unless otherwise stated, it is customary to treat work as occurring without its [[dissipation]] to the surroundings. Practically speaking, in all natural process, some of the work is dissipated by internal friction or viscosity. The work done by the system can come from its overall kinetic energy, from its overall potential energy, or from its internal energy.

功是一种以某种方式向系统传递能量或从系统传递能量的过程，其方式可以用作用在系统外部及其周围环境之间的宏观机械力来描述。'''<font color="#32CD32">例如，外部驱动的轴在系统内搅动，或外部施加的电场使系统材料极化，或活塞压缩系统。</font>'''除非另有说明，习惯上把功看作是在不影响周围环境的情况下发生的。实际上，在一切自然过程中，有些功是因内摩擦或粘黏而消失的。系统所做的功，可以来自于它的总动能，总势能或者它的内能。

做功是一种以某种方式向系统传递能量或从系统传递能量的过程，其方式可以用作用在系统外部及其周围环境之间的宏观机械力来描述。'''<font color="#32CD32">例如，外部驱动的轴在系统内搅动，或外部施加的电场使系统材料极化，或活塞压缩系统。</font>'''除非另有说明，习惯上把做功看作是在不影响周围环境的情况下发生的。实际上，在一切自然过程中，有些功是因内摩擦或粘黏而消失的。系统所做的功，可以来自于它的总动能，总势能或者它的内能。

The second law of thermodynamics indicates the irreversibility of natural processes and, in many cases, the tendency of natural processes to lead towards spatial homogeneity of matter and energy, and especially of temperature. It can be formulated in a variety of interesting and important ways.

The second law of thermodynamics indicates the irreversibility of natural processes and, in many cases, the tendency of natural processes to lead towards spatial homogeneity of matter and energy, and especially of temperature. It can be formulated in a variety of interesting and important ways.

 

It implies the existence of a quantity called the [[entropy]] of a thermodynamic system. In terms of this quantity it implies that

It implies the existence of a quantity called the [[entropy]] of a thermodynamic system. In terms of this quantity it implies that

It implies the existence of a quantity called the entropy of a thermodynamic system. In terms of this quantity it implies that

It implies the existence of a quantity called the entropy of a thermodynamic system. In terms of this quantity it implies that

{{quote|When two initially isolated systems in separate but nearby regions of space, each in [[thermodynamic equilibrium]] with itself but not necessarily with each other, are then allowed to interact, they will eventually reach a mutual thermodynamic equilibrium. The sum of the [[entropy|entropies]] of the initially isolated systems is less than or equal to the total entropy of the final combination. Equality occurs just when the two original systems have all their respective intensive variables (temperature, pressure) equal; then the final system also has the same values.}}

{{quote|When two initially isolated systems in separate but nearby regions of space, each in [[thermodynamic equilibrium]] with itself but not necessarily with each other, are then allowed to interact, they will eventually reach a mutual thermodynamic equilibrium. The sum of the [[entropy|entropies]] of the initially isolated systems is less than or equal to the total entropy of the final combination. Equality occurs just when the two original systems have all their respective intensive variables (temperature, pressure) equal; then the final system also has the same values.}}<br>

The second law is applicable to a wide variety of processes, reversible and irreversible. All natural processes are irreversible. Reversible processes are a useful and convenient theoretical fiction, but do not occur in nature.

The second law is applicable to a wide variety of processes, reversible and irreversible. All natural processes are irreversible. Reversible processes are a useful and convenient theoretical fiction, but do not occur in nature.

A prime example of irreversibility is in the transfer of heat by conduction or radiation. It was known long before the discovery of the notion of entropy that when two bodies initially of different temperatures come into thermal connection, then heat always flows from the hotter body to the colder one.

A prime example of irreversibility is in the transfer of heat by conduction or radiation. It was known long before the discovery of the notion of entropy that when two bodies initially of different temperatures come into thermal connection, then heat always flows from the hotter body to the colder one.