Revisiting the bell–jar demonstration

Abstract

The familiar bell–jar demonstration, commonly used to show that sound cannot travel in a vacuum, is revisited in this study. It is suggested that by emphasizing the different media present in this set-up, sound propagation in near-vacuum conditions can be made possible. In this way, the concept of sound propagation in this set-up can be examined in a nuanced manner. In a study involving upper-secondary students, the set-up has also been found to be helpful in addressing a few alternative conceptions related to sound propagation.

Demonstrating change from a drop-in space soundscape exhibit by using graffiti walls both before and after

“…Statistical uncertainties in proportions are estimated using the Clopper and Pearson (1934) conservative method based on the binomial distribution, where standard (68 %) errors are shown throughout.…”

“…Keiling et al, 2016). However, the belief by the public that space is completely empty in turn leads many to incorrectly think that there is absolutely no sound in space, reinforced by school science demonstrations such as the bell-jar experiment (see Caleon et al, 2013, for a nuanced discussion of this experiment and sound in near-vacuum conditions) or even popular culture like in the marketing to the movie 'Alien' ("in space no one can hear you scream"). Public engagement with this research area may help correct this fallacy.…”

Measuring the speed of sound in water

“…Conversely any sounds made within the water will be reflected at the surface rather than cross into a medium which is a thousandth of the density of the water. The classic demonstration with a bell in a jar being evacuated, works more because of the increasing density ratio between the gong and the thinning air (and between the air and the jar) than the inability of the remaining air to conduct sound, until extremely low pressures are reached [2].…”