Explanation:

Two halves of sphere are held together with a seemingly unbreakable clamping force, even though there is no clamping mechanism.

Lesson:

When the two hemispheres are brought together, there is air trapped on the inside. At the beginning, there is a balance between the air trapped on the inside and the air surrounding it. These two isolated regions of air push on the sphere with the same force so that one can simply pull the pieces apart. However, once the air on the inside is removed, using the vacuum pump, the balance is broken: the air on the outside pushes the hemispheres together with a much larger force.

Advanced Lesson:

We can calculate the force holding the two hemispheres together, much like our calculation from the vacuum chamber/balloon demonstration. The sphere has a radius of 2.5in and a surface area of 78.5 square inches. This results in a total force of 1155 lbs spread out over the outside surface of the sphere. If we pump down to .01 torr, the force pushing out from the inside will decrease from 1155 lbs to a fraction of a lb. So, one would have to be able to pull with a force of roughly 1,000 lbs to break the hemispheres apart.

UT Home | Physics Dept. Copyright © 2016 by The University of Texas at Austin