Lesson plan
Normal height
Normal heights (symbol H^* or H^N ; SI unit metre, m) is a type of height above sea level introduced by the Soviet scientist Mikhail Molodenskii. The normal height of a point is defined as the quotient of a point's geopotential number C (i.e. its geopotential difference with that of sea level), by the vertically averaged normal gravity: : H^N=C/\bar\gamma The average is evaluated along the normal potential's plumb line (a curve, approximated by the ellipsoidal normal, a straight line). The evaluation ranges from the Earth ellipsoid up to the point of interest; the procedure is thus recursive. Normal heights are slightly dependent upon the reference ellipsoid chosen. Normal gravity values are easier to compute compared to actual gravity, as one does not have to know the Earth's crust density. This is an advantage of normal heights compared to orthometric heights. The reference surface where normal heights are zero is called the quasi-geoid (or quasigeoid), a representation of mean sea level similar to the geoid and close to it, but lacking the physical interpretation of an equigeopotential surface.…
Article summary
Normal heights (symbol H^* or H^N ; SI unit metre, m) is a type of height above sea level introduced by the Soviet scientist Mikhail Molodenskii. The normal height of a point is defined as the quotient of a point's geopotential number C (i.e. its geopotential difference with that of sea level), by the vertically averaged normal gravity: : H^N=C/\bar\gamma The average is evaluated along the normal potential's plumb line (a curve, approximated by the ellipsoidal normal, a straight line). The evaluation ranges from the Earth ellipsoid up to the point of interest; the procedure is thus recursive. Normal heights are slightly dependent upon the reference ellipsoid chosen. Normal gravity values are easier to compute compared to actual gravity, as one does not have to know the Earth's crust density. This is an advantage of normal heights compared to orthometric heights. The reference surface where normal heights are zero is called the quasi-geoid (or quasigeoid), a representation of mean sea level similar to the geoid and close to it, but lacking the physical interpretation of an equigeopotential surface.…
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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