Rüchardt Experiment

Live Script illustrating how to sense the number of molecular degrees of freedom in a gas.

The Rüchardt experiment is an accessible test of the ideal gas law and thermodynamics[1]. A simple demonstration version of the experiment uses the motion of a metal sphere acting as a piston in an gas-filled tube connected to a gas-filled container. Released from rest, the ball executes a damped oscillation, the restoring force resulting from adiabatic compression of the gas. From the oscillation frequency, one can determine the ratio of the specific heats known as the adiabatic constant from which the effective number of molecular degrees of freedom may be found. This demonstration is one portal to a discussion of submicroscopic quantum phenomena.

This Live Script explores the principles and assumptions behind the Rüchardt experiment. It illustrates simple analysis of video of such oscillations with two different gases and compares of the ratio of adiabatic constants to expectation. It may interest students and instructors in physics. A 'Challenge' suggests an analysis of online videos for further exploration.