Bell in Bell Jar

A bell in a bell jar is a classic physics demonstration setup used to illustrate sound propagation and the effect of air pressure on sound. The apparatus consists of a metal bell placed on a base inside a transparent glass or plastic bell jar. When the jar is sealed and the air inside is pumped out to create a vacuum, the bell is rung. Due to the lack of air molecules to carry sound waves, the sound diminishes and eventually becomes inaudible as the vacuum strengthens. This shows that sound requires a medium, like air, to travel.