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To the definition of an ovoid: t tangent, s secant line. In projective geometry an ovoid is a sphere like pointset (surface) in a projective space of dimension d ≥ 3. Simple examples in a real projective space are hyperspheres . The essential geometric properties of an ovoid are:
The ellipsoid is a mathematically defined regular surface with specific dimensions. The geoid, on the other hand, coincides with that surface to which the oceans would conform over the entire Earth if free to adjust to the combined effect of the Earth's mass attraction (gravitation) and the centrifugal force of the Earth's rotation.
Many equations in relativistic physics appear simpler when expressed in geometric units, because all occurrences of G and of c drop out. For example, the Schwarzschild radius of a nonrotating uncharged black hole with mass m becomes r = 2m. For this reason, many books and papers on relativistic physics use geometric units.
The Hawking energy or Hawking mass is one of the possible definitions of mass in general relativity. It is a measure of the bending of ingoing and outgoing rays of light that are orthogonal to a 2- sphere surrounding the region of space whose mass is to be defined.
the mass–energy equivalence formula which gives the energy in terms of the momentum and the rest mass of a particle. The equation for the mass shell is also often written in terms of the four-momentum ; in Einstein notation with metric signature (+,−,−,−) and units where the speed of light c = 1 {\displaystyle c=1} , as p μ p μ ≡ p ...
has units of mass, and it is the only parameter in the Standard Model that is not dimensionless. It is also much smaller than the Planck scale and about twice the Higgs mass, setting the scale for the mass of all other particles in the Standard Model. This is the only real fine-tuning to a small nonzero value in the Standard Model.
The undulation of the geoid N is closely related to the disturbing potential T according to Bruns' formula (named after Heinrich Bruns): N = T / γ , {\displaystyle N=T/\gamma \,,} where γ {\displaystyle \gamma } is the force of normal gravity , computed from the normal field potential U {\displaystyle U} .
A surface mass on a surface given by the equation f (x, y, z) = 0 may be represented by a density distribution g(x, y, z) δ(f (x, y, z)), where / | | is the mass per unit area. The mathematical modelling can be done by potential theory , by numerical methods (e.g. a great number of mass points ), or by theoretical equilibrium figures.