An Atmospheric Pressure Ping-Pong “Ballometer”

Classroom experiments on atmospheric pressure focus largely on demonstrating its existence, often in a most impressive way. A series of amusing physics demonstrations is widely known and practiced by educators teaching the topic. However, measuring the value of atmospheric pressure $(Patm)$ is generally done in a rather mundane way, simply by reading some commercially produced meter. Even though students building a 35-ft high water barometer^1,2 is definitely instructive, as is the measurement of $Patm$ with much smaller gas-filled devices,^3,4 there exist hardly any physics lab exercises focused on the measurement of atmospheric pressure. This paper describes a modification of a well-known physics demonstration into an experiment that allows one to estimate atmospheric pressure quite accurately. Our simple and inexpensive apparatus can be used in lecture demonstrations or as a tool in an educational laboratory setting.