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  2. Linear density - Wikipedia

    en.wikipedia.org/wiki/Linear_density

    Consider a long, thin rod of mass and length .To calculate the average linear mass density, ¯, of this one dimensional object, we can simply divide the total mass, , by the total length, : ¯ = If we describe the rod as having a varying mass (one that varies as a function of position along the length of the rod, ), we can write: = Each infinitesimal unit of mass, , is equal to the product of ...

  3. Friedmann equations - Wikipedia

    en.wikipedia.org/wiki/Friedmann_equations

    The term Friedmann equation sometimes is used only for the first equation. [3] In these equations, R(t) is the cosmological scale factor, is the Newtonian constant of gravitation, Λ is the cosmological constant with dimension length −2, ρ is the energy density and p is the isotropic pressure.

  4. Mass flow rate - Wikipedia

    en.wikipedia.org/wiki/Mass_flow_rate

    The area required to calculate the mass flow rate is real or imaginary, flat or curved, either as a cross-sectional area or a surface, e.g. for substances passing through a filter or a membrane, the real surface is the (generally curved) surface area of the filter, macroscopically - ignoring the area spanned by the holes in the filter/membrane ...

  5. Current density - Wikipedia

    en.wikipedia.org/wiki/Current_density

    In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. [1] The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point.

  6. Number density - Wikipedia

    en.wikipedia.org/wiki/Number_density

    The number density (symbol: n or ρ N) is an intensive quantity used to describe the degree of concentration of countable objects (particles, molecules, phonons, cells, galaxies, etc.) in physical space: three-dimensional volumetric number density, two-dimensional areal number density, or one-dimensional linear number density.

  7. Schwarzschild radius - Wikipedia

    en.wikipedia.org/wiki/Schwarzschild_radius

    Stellar black holes have much greater average densities than supermassive black holes. If one accumulates matter at nuclear density (the density of the nucleus of an atom, about 10 18 kg/m 3; neutron stars also reach this density), such an accumulation would fall within its own Schwarzschild radius at about 3 M ☉ and thus would be a stellar ...

  8. Density - Wikipedia

    en.wikipedia.org/wiki/Density

    Water density calculator Archived July 13, 2011, at the Wayback Machine Water density for a given salinity and temperature. Liquid density calculator Select a liquid from the list and calculate density as a function of temperature. Gas density calculator Calculate density of a gas for as a function of temperature and pressure.

  9. Density of air - Wikipedia

    en.wikipedia.org/wiki/Density_of_air

    To calculate the density of air as a function of altitude, one requires additional parameters. For the troposphere, the lowest part (~10 km) of the atmosphere, they are listed below, along with their values according to the International Standard Atmosphere , using for calculation the universal gas constant instead of the air specific constant: