Pressure, symbolized as P or p in physics, measures the amount of continuous perpendicular force applied to a surface. Pressure is calculated by dividing the amount of force (typically measured in newtons) by the surface area that the force is being applied to. The SI unit for pressure is the pascal, which is the equivalent of one newton of square force per one square meter of surface area. However, pressure is often measured in non-SI units when calculating liquid or atmospheric pressure. An example of a common non-SI unit of pressure is the bar, a unit equivalent to 100,000 pascals that is most often utilized to measure the Earth's atmospheric pressure. Pressure is also a unit of ideal gas law, varying linearly with absolute temperature and the amount of substance, and inversely with the volume of the gas.
Does anybody know the etymology of the phrase "sweet dreams"? I tried googling but did not find anything satisfying. Is this a relatively new phrase of the modern world or has this been in use for some time? I think it's the latter one. Answer The OED has the interjection as "a farewell to someone going to bed" from the 20th century: 1908 Sears Roebuck Catal. 198/1 Tenor Solos..Good Bye, Sweet Dreams, Good Bye. But it goes back until at least the 19th and possibly 18th centuries. John Wolcot, writing under the pseudonym of Peter Pindar, used it in his poem "Orson and Ellen; A Legendary Tale" published in 1801: Also from 1801 in The infernal Quixote (Page 287) by Charles Lucas: In the March 1776 of The Universal Magazine was published "The Serenade. A Pastoral Tale. From the German of Gesner" , where the shepherd Daphnis watches over his beloved as she sleeps and sings: The same tale appears in 1776's as Idyl XI, " Daphnis ...
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