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New answers tagged definition

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An addition to Daniel's answer: It regularly happens that a certain definition isn't applicable when talking about liquids and gases. For example, almost all definitions in thermodynamics are defined for closed systems, which is rarely applicable in the real world. To overcome this, there is the notion of a control volume. For this, we basically take a ...

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The pressure of a gas is defined as the force the gas would exert upon a surface or container. However, there is no need for a container for pressure to exist. For instance, the air you're breathing right now (unless you're in an airplane or submarine) has pressure due to the column of atmosphere above you. Stars are balls of gas (plasma, actually) that are ...

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By its definition, the Einstein tensor is always defined to be $\nabla G = 0$, via the Bianchi identity. Here's the proper definition of a spacetime in general relativity : A spacetime is defined by a triplet $(\mathcal{M}, g, \nabla)$ of a manifold $\mathcal{M}$, a metric upon that manifold $g$ (or alternatively it can be done with a tetrad field) and a ...

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Yes, that is correct in a very strict and narrow sense. You can totally use the term "charge" to mean a particle which holds a certain fundamental electric charge. In a much broader sense, please notice that a current can be said to flow across a capacitor (a break in a circuit!) even when charges cannot move between the terminals of the capacitor. ...

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Yes, that's the definition. More precisely, current is the amount of charge (measured in Coulomb) flowing past a cross section per time interval (measured in seconds).

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In the 1800's the AU was connected to: the time average of 1 divided by the Earth-Sun, and that is the reason Gauss's constant occurred (until 2012) in the calculation of the AU. The reciprocal of the distance was used because it has less of a linear tread and also because it is not as dependent on the eccentricity (which has a large ~linear trend over the ...

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to be more specific about the definition of charge, charge is an intrinsic property of inherent matter. As we all know the mass which is considered as the fundamental property of every particle in this universe, electric charge is considered as the fundamental property of the particle that is used for electrostatic purposes.from the Franklin`s view he ...

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A gas can expand by filling more volume than before. Like a balloon in a pressure chamber where the pressure is suddenly lowered. No net motion (no flow) happens here. A water stream can flow continously without simultaneous expansion. Consider a circular stream that ends where it starts. As a bathtub where there is a big plastic bucket in the center. By ...

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The 2nd law is a restriction on the class of constitutive relations that would specify/describe the material behavior, here heat conduction. Fourier's law of heat conduction is not a "law" or part of a "law", it is rather a constitutive relation describing material properties for which the 2nd law applies. The relationship to the 2nd law is manifested in the ...

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When we talk about there being multiple statements of the second law what we mean is that the different statements are logically equivalent, i.e. we may postulate any valid statement of the second law we choose and derive all the others. So we can deduce the increase of entropy by assuming Clausius' statement, but we can also assume the increase in entropy ...

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Fourier's law $\vec\jmath=-\kappa\vec\nabla T$ implies $$\frac{dS}{dt}=\int d^3x \frac{\kappa}{T^2}(\vec\nabla T)^2 + \ldots$$ where $\ldots$ is other sources of dissipation (viscosity etc.). This result requires a little effort, but it is explained in standard fluid dynamics text books (chapter V of Landau, for example). Then the second law of ...

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