Mathematics and Society - OS X Lion Server

Above every person is a tall column of air pushing downwith an amazing force. This causes air pressure.A column of air extending through the atmosphere havinga cross sectional area of 1 cm Z has a mass of about 1,034grams. So the pressure caused by air is 1,034 g/cm Z atsea level. (14.7 pounds/in Z ),,I, , , ,, ,l"isQ-"\''''''' '("IIISeveral simple classroom demonstrations to show this pressure are outlined below.TII\lCAt\)HOT. ..:\;f;:./:: STEAMPLATE.-.AIR PRESSUREBE. SURE. II-\E P"'I"ER ISSMOOTHED COWl.] WITH NOAIR pOCKETS UNOE.RNE.A'H.Put about 2 em of water in a rather large metalcan that can be sealed with a lid or rubber stopper.Place the open can with water on a hot plate untilthe water boils for several minutes.This willdrive out most of the air leaving only steam in thecan.Remove the can from the heat and quickly sealit. As the can cools the steam condenses, creatinga partial vacuum inside the can.With little airpressure left inside the can will be collapsed from (the outside pressure.Cover a wooden slat (about the size of a ruler)with a large sheet of paper.newspaper is sufficient.A layer or two ofLet about 5 em of thisslat stick out from under the paper and over theedge of the table. Smooth down the paper. With ahard sharp blow strike the exposed end of the woodenslat.Due to the air pressure above the paper thewooden slat will break without tearing the paper.IIIL-/_~/" :".... :.:" .Completely fill a glass with water.Carefully place a heavy piece of smoothcardboard on top the glass of water.Hold the cardboard and invert the glassof water.Keeping a hold on the glassstop supporting the cardboard.332 By calculating the surface area involved students cancalculate the air pressure in each of these cases.It willmagically seem to hold the water in theinverted glass.GLASS H[LOIt\) AIR WA'ER It-lSID£GLA~"'> E'i.E.RTS. ..... '. . .. A. DOWI\l\.JARDFORCE.~ AIR PRESSORE ONT THE. OUTSIDEEY.ERTS A GREA,ERUP\.JARD FORCE.(