  We consider a heavy external object moving in an ideal gas of light
particles. Collisions with the gas particles transfer momentum to the object,
leading to a force that is proportional to the object's velocity but in the
opposite direction. In an ideal classical gas at temperature $T$, the force
acting on the object is proportional to $\sqrt{T}$. Quantum statistics causes a
deviation from the $\sqrt{T}$-dependence and shows that the force scales with
$T^2$ at low temperatures. At $T=0$, the force vanishes in a Bose gas but is
finite in a Fermi gas.
