Sunday, January 22, 2017

Galileo Galilei and air pressure

Galileo is believed to have been one of the first to suggest an experiment that tested the relationship between the density of the liquid and the height of the column.

In 1640, Galileo conducted a suction-pump experiment at a pubic well together with his two assistants: Evangelista Torricelli and Giovanni Baliani.

He lowered a long tube into the well’s and from the well, Galileo’s tube draped up over a wooden cross-beam three meters above the well’s wall and then downs to a hand-powered pump held by two assistants. His assistants pumped the pump’s wooden handler, slowly sucking air out of Galileo’s tube, pulling water higher into the tube.

Galileo Galilei
They pumped until the tube flattered line a run-over drinking straw. In his Two New Sciences he noted that no matter how hard they worked water would not rise more than 9.7 meters above the well’s water level. It was the same in every test.

Galileo commented that a suction pump could not lift water more than 10 m so there appeared to be a limit to this abhorrence. Galileo realized that this had important consequences for suction pumps. Suction pumps do not ‘suck’ up water as was commonly thought.

He became satisfied that this was universal law of nature and that the rise of water to a certain height in pumps exhausted of air, was neither owing to nature’s horror of a vacuum or to the power of suction but to atmospheric pressure.

It is atmospheric pressure on the surface of the water that pushes water into the pump and to do this air must first be removed from the pump to create a vacuum – a process own as ‘priming’.

No very useful results, however were expected from this discovery, until at a later date, Torricelli adopted and greatly extended it.
Galileo and air pressure
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