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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 ( quadrics ). The essential geometric properties of an ovoid O {\displaystyle {\mathcal {O}}} 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.
To the definition of an oval in a projective plane To the definition of an ovoid. In a projective plane a set Ω of points is called an oval, if: Any line l meets Ω in at most two points, and; For any point P ∈ Ω there exists exactly one tangent line t through P, i.e., t ∩ Ω = {P}.
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} .
Geophysics emerged as a separate discipline only in the 19th century, from the intersection of physical geography, geology, astronomy, meteorology, and physics. [ 46 ] [ 47 ] The first known use of the word geophysics was in German ("Geophysik") by Julius Fröbel in 1834. [ 48 ]
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.
For the mass attraction effect by itself, the gravitational acceleration at the equator is about 0.18% less than that at the poles due to being located farther from the mass center. When the rotational component is included (as above), the gravity at the equator is about 0.53% less than that at the poles, with gravity at the poles being ...
The equation = is an equation of a line in the projective plane (see definition of a line in the projective plane), and is called the line at infinity. The equivalence classes, , are the lines through the origin with the origin removed. The origin does not really play an essential part in the previous discussion so it can be added back in ...