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Torricelli concluded that the mercury fluid in the tube is aided by the atmospheric pressure that is present on the surface of mercury fluid on the dish. He also stated that the changes of liquid level from day to day are caused by the variation of atmospheric pressure. The empty space in the tube is called the Torricellian vacuum. [3] 760 mmHg ...
Torricelli's work led to first speculations about atmospheric pressure, and to the corollary invention of the mercury barometer (from the Greek word baros, meaning weight [16]) -- the principle of which was described as early as 1631 by René Descartes, although there is no evidence that Descartes ever built such an instrument. [17]
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa ), which is equivalent to 1,013.25 millibars , [ 1 ] 760 mm Hg , 29.9212 inches Hg , or 14.696 psi . [ 2 ]
The laws describing the behaviour of gases under fixed pressure, volume, amount of gas, and absolute temperature conditions are called gas laws.The basic gas laws were discovered by the end of the 18th century when scientists found out that relationships between pressure, volume and temperature of a sample of gas could be obtained which would hold to approximation for all gases.
In medicine, hydrostatic pressure in blood vessels is the pressure of the blood against the wall. It is the opposing force to oncotic pressure. In capillaries, hydrostatic pressure (also known as capillary blood pressure) is higher than the opposing “colloid osmotic pressure” in blood—a “constant” pressure primarily produced by ...
1667 – Robert Hooke builds another type of anemometer, called a pressure-plate anemometer. [22] 1686 – Edmund Halley presents a systematic study of the trade winds and monsoons and identifies solar heating as the cause of atmospheric motions. – Edmund Halley establishes the relationship between barometric pressure and height above sea ...
For gases, pressure is sometimes measured not as an absolute pressure, but relative to atmospheric pressure; such measurements are called gauge pressure. An example of this is the air pressure in an automobile tire, which might be said to be "220 kPa (32 psi)", but is actually 220 kPa (32 psi) above atmospheric pressure. Since atmospheric ...
The Magdeburg hemispheres are a pair of large copper hemispheres with mating rims that were used in a famous 1654 experiment to demonstrate the power of atmospheric pressure. When the rims were sealed with grease and the air was pumped out, the sphere contained a vacuum and could not be pulled apart by teams of horses. Once the valve was opened ...