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In addition to Newton's Law of Gravity in the physical sciences, there were other antecedents to Reilly's "law" of retail gravity. In particular, E.C. Young in 1924 described a formula for migration that was based on the physical law of gravity, and H.C. Carey had included a description of the tendency of humans to "gravitate" together in an 1858 summary of social science theory.
Back-of-the-envelope calculation. A back-of-the-envelope calculation is a rough calculation, typically jotted down on any available scrap of paper such as an envelope. It is more than a guess but less than an accurate calculation or mathematical proof. The defining characteristic of back-of-the-envelope calculations is the use of simplified ...
The first equation shows that, after one second, an object will have fallen a distance of 1/2 × 9.8 × 1 2 = 4.9 m. After two seconds it will have fallen 1/2 × 9.8 × 2 2 = 19.6 m; and so on. The next-to-last equation becomes grossly inaccurate at great distances. If an object fell 10 000 m to Earth, then the results of both equations differ ...
Stochastic differential equations originated in the theory of Brownian motion, in the work of Albert Einstein and Marian Smoluchowski in 1905, although Louis Bachelier was the first person credited with modeling Brownian motion in 1900, giving a very early example of a stochastic differential equation now known as Bachelier model.
A good's price elasticity of demand ( , PED) is a measure of how sensitive the quantity demanded is to its price. When the price rises, quantity demanded falls for almost any good ( law of demand ), but it falls more for some than for others. The price elasticity gives the percentage change in quantity demanded when there is a one percent ...
Newsvendor model. The newsvendor (or newsboy or single-period[ 1] or salvageable) model is a mathematical model in operations management and applied economics used to determine optimal inventory levels. It is (typically) characterized by fixed prices and uncertain demand for a perishable product. If the inventory level is , each unit of demand ...
Stiffness. Extension of a coil spring, caused by an axial force, Stiffness is the extent to which an object resists deformation in response to an applied force. [ 1] The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is. [ 2]
Lists of physics equations. In physics, there are equations in every field to relate physical quantities to each other and perform calculations. Entire handbooks of equations can only summarize most of the full subject, else are highly specialized within a certain field. Physics is derived of formulae only.