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where L and w are, respectively, the perimeter and the width of any curve of constant width. A = π r 2 {\displaystyle A=\pi r^{2}} where A is the area of a circle .
By making this assumption, g takes the following form: = (i.e., the direction of g is antiparallel to the direction of r, and the magnitude of g depends only on the magnitude, not direction, of r). Plugging this in, and using the fact that ∂ V is a spherical surface with constant r and area 4 π r 2 {\displaystyle 4\pi r^{2}} ,
The result reported by Charles Hutton (1778) suggested a density of 4.5 g/cm 3 (4 + 1 / 2 times the density of water), about 20% below the modern value. [16] This immediately led to estimates on the densities and masses of the Sun , Moon and planets , sent by Hutton to Jérôme Lalande for inclusion in his planetary tables.
A mathematical constant is a key number whose value is fixed by an unambiguous definition, often referred to by a symbol (e.g., an alphabet letter), or by mathematicians' names to facilitate using it across multiple mathematical problems. [1]
The Einstein field equations (EFE) may be written in the form: [5] [1] + = EFE on the wall of the Rijksmuseum Boerhaave in Leiden, Netherlands. where is the Einstein tensor, is the metric tensor, is the stress–energy tensor, is the cosmological constant and is the Einstein gravitational constant.
For two bodies, the parameter may be expressed as G(m 1 + m 2), or as GM when one body is much larger than the other: = (+). For several objects in the Solar System, the value of μ is known to greater accuracy than either G or M. The SI unit of the standard gravitational parameter is m 3 ⋅s −2.
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.
r is the radius of the sphere, h is the height of the cap, and; sr is the unit, steradian, sr = rad 2. Because the surface area A of a sphere is 4πr 2, the definition implies that a sphere subtends 4π steradians (≈ 12.56637 sr) at its centre, or that a steradian subtends 1/4π ≈ 0.07958 of a sphere.