Pressure Vacuum Historical Development Rhine Feb 2011 Historical

Pressure & Vacuum Historical Development Rhine Feb 2011

Historical Timeline – Ancient Greece • Aristotle – Natural state of materials – Hot or cold air (gravitas & levitas) – Nature abhors a vacuum – His ideas widely held for next 2000 years!! • Archimedes – Buoyancy & fluid displacement – Eureka moment

Historical Timeline - Renaissance

Necessity of the mother of invention (or scientific discovery) Galileo (1564 – 1642) • Miners used suction pumps to • • • pump water out of mining shafts Pumps could not work at depths > ~ 30 ft Galileo discussed problem issue “Dialogue of The Two New Sciences” (1638) He thought water column “broke” at certain height – Could not support weight? – Interstitial vacuum holding matter together?

Water collapses in pipe Gasparto Berti (1600 – 1643) • 40 foot lead pipe capped • • at top Put in trough of water When capped end elevated, water “collapsed” to 32 ft column What was left in top? ? One of Galileo’s “Roman triumverate”, Rafaello Magiotti witnessed event

Evangelista Torricelli (1608 – 1647) • Expanded on Berti’s experimentation • Used mercury in glass tube – column collapsed to ~ 760 mm • Like Berti, he claimed vacuum must be in void at top. Why?

Letter to Michelangelo Ricci in 1644 Evangelista Torricelli (1608 – 1647) • Discussed principle of his • • • experiment with mercury “We live at the bottom of a sea of air” A column of air 50 miles high has weigh (gravity) and exerts pressure on mercury in dish Pressure on dish can only support column of equal weight/area (pressure)

Wind and Vaccum Evangelista Torricelli (1608 – 1647) • Proposed that void at top of column is a • • • vacuum Torricelli is credited with creating first sustained vacuum and for invention of barometer Torricelli noted that winds must be created by geographical differences in pressure: wind = fluid (air) moves from high to low Earlier in career he also experimentally showed that speed of fluid flow from hole in side of container is proportional to the square root of the depth (pressure) – special case of Daniel Bernoulli’s fluid flow law published in 1738

Before elevators, had to use stairs! Blaise Pascal (1623 – 1662) • Convincing demonstration of mercury barometer – Moved barometer from ground level to top of tall tower – noted drop in mercury level – Moved barometer from ground level to top of nearby mountain – even larger drop • Provided more compelling arguments for vacuum above column

What happens when you pump all of the air out of a barrel? Otto von Guericke (1602 -1686) • Really, he did this! • Used suction pump to “pull” air out - barrels • imploded! Invented first efficient vacuum pumps

How strong is a vacuum? Otto von Guericke (1602 -1686) • • • Invented Magdeburg Spheres Pumped out air in two hemispheres, “gluing” them together Higher external air pressure vs. lower internal Hitch both ends to teams of horses Amazed people by separating sphere with simple twist of a pressure valve Like Torricelli, von Guericke also noted that wind created by differences in air pressure (obervations from separating spheres)