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This is an accepted version of this page This is the latest accepted revision, reviewed on 6 February 2025. Law of physics and chemistry This article is about the law of conservation of energy in physics. For sustainable energy resources, see Energy conservation. Part of a series on Continuum mechanics J = − D d φ d x {\displaystyle J=-D{\frac {d\varphi }{dx}}} Fick's laws of diffusion Laws ...
Out of a total of 28,400 terawatt-hours (96.8 × 10 ^ 15 BTU) of energy used in the US in 1999, 10.5% was used in food production, [3] with the percentage accounting for food from both producer and primary consumer trophic levels. In comparing the cultivation of animals versus plants, there is a clear difference in magnitude of energy efficiency.
An adiabatic wall between the two systems is 'permeable' only to energy transferred as work; at mechanical equilibrium the rates of transfer of energy as work between them are equal and opposite. If the wall is a simple wall, then the rates of transfer of volume across it are also equal and opposite; and the pressures on either side of it are ...
Energy conversion efficiency depends on the usefulness of the output. All or part of the heat produced from burning a fuel may become rejected waste heat if, for example, work is the desired output from a thermodynamic cycle. Energy converter is an example of an energy transformation.
The second law of thermodynamics is a physical law based on universal empirical observation concerning heat and energy interconversions.A simple statement of the law is that heat always flows spontaneously from hotter to colder regions of matter (or 'downhill' in terms of the temperature gradient).
[7] 100×10 15 grams of carbon/year fixed by photosynthetic organisms, which is equivalent to 4×10 18 kJ/yr = 4×10 21 J/yr of free energy. Cellular respiration is the reverse reaction, wherein energy of plants is taken in and carbon dioxide and water are given off.
Energy flux is the rate of transfer of energy through a surface. The quantity is defined in two different ways, depending on the context: Total rate of energy transfer (not per unit area); [1] SI units: W = J⋅s −1. Specific rate of energy transfer (total normalized per unit area); [2] SI units: W⋅m −2 = J⋅m −2 ⋅s −1:
Especially in the field of radiation damage in detectors, the term "non-ionizing energy loss" (NIEL) is used as a term opposite to the linear energy transfer (LET), see e.g. Refs. [13] [14] [15] Since per definition nuclear stopping power does not involve electronic excitations, NIEL and nuclear stopping can be considered to be the same ...