In 1654 Otto von Guericke, inventor of the air pump, gave a demonstration before the noblemen of the Holy Roman Empire in which two teams of eight horses could not pull apart two evacuated brass hemispheres. Assume that the hemispheres have thin walls, so that R in the figure may be considered both the inside and outside radius. taking R as 31 cm, the inside pressure as 0.10 atm, and the outside pressure as 1.0 atm, find the force magnitude the teams of horses would have had to exert to pull apart the hemispheres.
Explanation / Answer
the inside and outside radii are = R =42 cm =42*10^-2m the outer and inner areas of each hemisphere is A =R^2 =3.14*(42*10^-2)^2 =0.553896 m^2 the known formula pressure = force /area force = pressure *area the force required to each team of the horses is F = area *(pressure difference between outside and inside) required force for each team of horses is F =0.553896*(1-0.13) = 0.48188952N