Inside a bell jar there are no air molecules. Credit: DLR (CC-BY 3.0)
In 1654, Otto von Guericke, the mayor of Magdeburg, impressed the Emperor with a spectacular experiment on vacuums: 16 horses could not pull apart what was being held together by air pressure alone – two halves of a large copper sphere. How was this possible? Can a space ever be truly empty? And what does this have to do with weightlessness?
Examine how air molecules influence the behaviour of objects and physical processes with a glass tube and a bell jar. Will a feather drop or float in a vacuum? Does a balloon stay the same? What do the results tell you about the nature of vacuums? What should we consider when building equipment for use in a vacuum? Which problems might arise when constructing satellites and spacecraft?
Vacuum technology is an indispensable part of scientific research. Many physical, chemical and biological processes can only be studied in a vacuum. The performance capability of rocket engines, for example, is tested in a large vacuum test facility. The industrial sector is also reliant on vacuum. Foods such as coffee or dried fruits are conserved through vacuums and various technological appliances like vacuum cleaners and pumps used in medical engineering also work with vacuum.
Much a(ir-)do about nothing ?
Testing Otto von Guericke's experiment in the DLR_School_Lab. Credit: DLR
Find out for yourselves how strong the air pressure is when you try and pull apart our replica of the Magdeburg hemispheres. It is not only air that is made up of molecules, but water, too. How can we influence the behaviours of gases and fluids? Does water always boil at 100°C? And can you explain why we would have to boil an egg longer if we were on Mount Everest?