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A pound lock has a chamber with gates at both ends that control the level of water in the pound. In contrast, an earlier design with a single gate was known as a flash lock. [4] Pound locks were first used in China during the Song dynasty (960–1279 CE), having been pioneered by the Song politician and naval engineer Qiao Weiyue in 984. [5]
A short pound on the Chesterfield Canal in England, United Kingdom. A canal pound (from impound), [1] reach, or level (American usage), is the stretch of level water impounded between two canal locks. Canal pounds can vary in length from the non-existent, where two or more immediately adjacent locks form a lock staircase, to many kilometres/miles.
The principle of coherence was successfully used to define a number of units of measure based on the CGS, including the erg for energy, the dyne for force, the barye for pressure, the poise for dynamic viscosity and the stokes for kinematic viscosity. [29]
The Pound–Rebka experiment monitored frequency shifts in gamma rays as they rose and fell in the gravitational field of the Earth. The experiment tested Albert Einstein 's 1907 and 1911 predictions, based on the equivalence principle , that photons would gain energy when descending a gravitational potential, and would lose energy when rising ...
English-speaking countries also used a system of units of fluid measure, or in modern terminology volume units, based on the apothecaries' system. Originally, the terms and symbols used to describe the volume measurements of liquids were the same as or similar to those used to describe weight measurements of solids [33] (for example, the pound by weight and the fluid pint were both referred to ...
The pound lock holds water between two gates, and is considerably easier to navigate. Pound locks have been built in China since 983, in the Netherlands from 1065 and in Britain from the 1560s. Nevertheless, a few flash locks remained after the introduction of pound locks.
As such, these are ready extensions of any system of containing length, mass, time. Stephen Dresner [7] gives the derived electrostatic and electromagnetic units in both the foot–pound–second and foot–slug–second systems. In practice, these are most associated with the centimetre–gram–second system.
Systems of measure either define mass and derive a force unit or define a base force and derive a mass unit [1] (cf. poundal, a derived unit of force in a mass-based system). A slug is defined as a mass that is accelerated by 1 ft/s 2 when a net force of one pound (lbf) is exerted on it.