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The higher the energy density of the fuel, the more energy may be stored or transported for the same amount of volume. The energy of a fuel per unit mass is called its specific energy. The adjacent figure shows the gravimetric and volumetric energy density of some fuels and storage technologies (modified from the Gasoline article).
where: is the rate of change of the energy density in the volume. ∇•S is the energy flow out of the volume, given by the divergence of the Poynting vector S. J•E is the rate at which the fields do work on charges in the volume (J is the current density corresponding to the motion of charge, E is the electric field, and • is the dot product).
However, any type of energy has its direction of movement in space, as well as its density, so energy flux vectors can be defined for other types of energy as well, e.g., for mechanical energy. The Umov–Poynting vector [ 11 ] discovered by Nikolay Umov in 1874 describes energy flux in liquid and elastic media in a completely generalized view.
The density of states related to volume V and N countable energy levels is defined as: = = (()). Because the smallest allowed change of momentum for a particle in a box of dimension and length is () = (/), the volume-related density of states for continuous energy levels is obtained in the limit as ():= (()), Here, is the spatial dimension of the considered system and the wave vector.
Energy density per unit mass J⋅kg −1: L 2 T −2: intensive Specific heat capacity: c: Heat capacity per unit mass J/(K⋅kg) L 2 T −2 Θ −1: intensive Specific volume: v: Volume per unit mass (reciprocal of density) m 3 ⋅kg −1: L 3 M −1: intensive Spin: S: Quantum-mechanically defined angular momentum of a particle kg⋅m 2 ⋅s ...
1.80 [16] 1.26: battery, Fluoride-ion [citation needed] 1.7: 2.8: battery, Hydrogen closed cycle H fuel cell [17] 1.62: Hydrazine decomposition (as monopropellant) 1.6: 1.6: Ammonium nitrate decomposition (as monopropellant) 1.4: 2.5: Thermal Energy Capacity of Molten Salt: 1 [citation needed] 98% [18] Molecular spring approximate [citation ...
physics, engineering (Damping ratio of oscillator or resonator; energy stored versus energy lost) Relative density: RD = hydrometers, material comparisons (ratio of density of a material to a reference material—usually water)
The cosmological constant has the same effect as an intrinsic energy density of the vacuum, ρ vac (and an associated pressure). In this context, it is commonly moved to the right-hand side of the equation using Λ = κρ vac. It is common to quote values of energy density directly, though still using the name "cosmological constant".