To demonstrate force arising from the atmospheric pressure of air.
Magdeburg hemisphere apparatus with vacuum pump cart.
Push the hemispheres together and twist while to seat the grease seals. Close the valve and remove the◙vacuum connection before attempting to pull the hemispheres apart.◙
A mechanical pump is used to evacuate the air from inside a pair of sealed hemispheres. Ropes on the two hemispheres allow two groups of students to attempt to pull the hemispheres apart against the force produced by the atmospheric air pressure. The hemispheres have a diameter of about 5 inches, thus requiring a force of over 250 pounds to separate them when fully evacuated. A safety restraint holds the two hemispheres so that if the pressure releases they will not separate entirely. Three students pulling on each rope may be able to separate the hemispheres.◙
Ernest Hammond, Demonstration of Atmospheric Pressure, TPT 3, 67, (1965).