Suppose that a piston of nonzero mass encloses an ideal gas in a vertical cylinder. The piston and
cylinder are thermally insulated so that no energy is lost by heat transfer to the surroundings. If
the piston is set into motion, it oscillates like a block on a spring. However, the motion is damped
because the gas density and pressure immediately adjacent to the piston are higher or lower than the
bulk values, depending on whether the piston is compressing or expanding the gas, respectively. That
automatically gives rise to a drag force linear in the velocity of the piston. It is not necessary
to add extra dissipative terms such as kinetic friction between the piston and cylinder, or
viscosity of the gas, to damp out the motion of the piston. The ideas should thus be helpful to
undergraduate students performing a Rüchardt experiment to measure the ratio of the heat capacities
of a gas.