In existographies, Simon Stevin (1548-1620) (IQ:175|#282) (GME:#) (CR:10) was a Dutch mathematician, engineer, and polymath, noted for his 1586 Statics and Hydrostatics, wherein he is said to have given the first complete statement of the impossibility of perpetual motion, and also derived the notion of the vectorial decomposition of forces, according to which force that must be exerted along the line of greatest slope to support a given weight on an inclined plane.
-
Earth | Weight
In 1586, Stevin, in his Statistics, calculated the weight of the earth to be 2x10E24 lbs, which is cited, as cited by Otto Guericke (1663), as one of the four main people to do so, along with Forerius, Scipione Chiaramonti, and Mersenne. [2]

Falling bodies
In 1586, Stevin conducted an experiment wherein he dropped two lead balls, one ten times heavier than the other, from a height of 30 feet onto a board, finding that the two balls hit the board at the same time, a finding contrary to the opinion of Aristotle, who held that the heavier ball would strike the board first. [4] This experiment was later repeated and or improved upon by Galileo.

Decimals
Stevin, thought he did not invent the decimal system, is generally credited with the promotion and popularization of its usage in everyday practice. The 1608 English translation of Stevin’s work Disme, The Arts of Tenths or Decimal Arithmetike, by Robert Norton, is said to have inspired American philosopher Thomas Jefferson to propose a decimal monetary unit for the new United States of America. The tenth of a dollar is still referred to as a “dime.”

Hydrostatics | Fluid mechanics
Steven, supposedly, found that the pressure of water was proportional to its depth. [4] This idea was later expanded on by Evangelista Torricelli and Blaise Pascal.

Some conjecture that much of logic of Pascal’s law, in fluid mechanics, was derived from the work of Stevin. [3]

Quotes | On
The following are quotes on Stevin:

“The thirteenth century author, possibly Jordanus Nemorarius, of De Ratione Ponderis, had thought of investigating the weight of an object resting upon an inclined plane. This idea the Netherlander Simon Stevin developed in 1586 into the ‘parallelogram of forces’, demonstrating that three forces in equilibrium at a point can represent both in magnitude and in direction by the sides of a triangle.”
— Richard Kirby (1956), Engineering in History [4]

Hooke’s most important work in the spring of 1685 was a long paper, read to the Royal Society in Feb and early Mar, on land and water vehicles and the problem of friction. He was responding to reports from Oxford of an experimental cart with five-inch wheels, but the main subject of his discourse was the very efficient wheeled sailing chariot made by Simon Stevin for Prince Maurice of Orange early in the seventeenth century. Stevin's chariot had carried a load of twenty-eight passengers forty-two miles in two hours, and seemed to be 'the swiftest Carriage yet known, for so great a Burthen, and for so long a way.”
— Stephen Inwood (2002), The Man Who Knew Too Much (pg. 356)

Stevin’s work on windmills, his original theoretical contributions to statics and hydrostatics, and the unity of theory and practice in his work make him in mechanics the first true successor of Archimedes in the Renaissance.”
— Teun Koetsier (2010), “Simon Stevin and the Rise of Archimedean Mechanics in the Renaissance” (Ѻ)

Quotes | By
The following are quotes by Stevin:

“Disme [decimals] is a kind of arithmeticke [arithmetic], invented by the tenth progression, consisting in characters of cyphers; whereby a certain number is described, and by which also all accounts which happen to humane affayres [affairs], are dispatched by whole numbers, without fractions or broken numbers.”
— Simon Stevin (c.1590), Publication

References
1. (a) Stevin, Simon. (1586). Statics and Hydrostatics (Beghinselen Der Weegkunst). Publisher.
(b) Mach, Ernst. (1911). History and Root of the Principle of Conservation of Energy. Open Court Publishing.
(c) Mirowski, Philip. (1989). More Heat than Light: Economics as Social Physics, Physics as Nature’s Economics (pg. 15). Cambridge University Press.
2. Guericke, Otto. (1663). The Vacuum of Space (De Spatio Vacuo). Unpublished; New Magdeburg Experiments on the Vacuum of Space (Ottonis De Guericke Experimenta Nova (ut vocantur) Magdeburgica de Vacuo Spatio) (preface, pdf) (pg. 206). Janssonius a Waesberge, 1672.
3. Knowles, W.E. (1964). The History of the Barometer (Stevin, pg. 53). Publisher.
4. Kirby, Richard; Withington, Sidney; Darling, Arthur; and Kilgour, Frederick. (1956). Engineering in History (pg. 127). Courier, 1990.