1. In 1656, the Burgmeister (mayor) of the town of Magdeburg, Germany, Otto Von

Question

1. In 1656, the Burgmeister (mayor) of the town of Magdeburg, Germany, Otto Von Guericke, carried out a dramatic demonstration of the effect resulting from evacuating air from a container. It is the basis for this problem. Two steel hemispheres of radius 0.390 m (1.28 feet) with a rubber seal in between are placed together and air pumped out so that the pressure inside is 19.00 millibar. The atmospheric pressure outside is 970 millibar. Calculate the force required to pull the two hemispheres apart.

[Note: 1 millibar=100 N/m2. One atmosphere is 1013 millibar = 1.013×105 N/m2 ]

2. Two equal teams of horses, are attached to the hemispheres to pull it apart. If each horse can pull with a force of 1420N (i.e., about 319 lbs), what is the minimum number of horses required?

Explanation / Answer

  The contact area between the hemispheres is (pi x .390^2) = 0.477m^2.

Pressure difference = (970 - 19) = 951 millibars.

(951 x 100) = 95100N/m^2.

(95100 x 0.477) = 45362.7N. force required to part the hemispheres.

(45362.7/1420) = 31.94 horses each side, = 63.89 horses.

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