  Electrons moving in a conductor can transfer momentum to the lattice via
collisions with impurities and boundaries, giving rise to a fluctuating
mechanical stress tensor. The root-mean-squared momentum transfer per
scattering event in a disordered metal (of dimension L greater than the mean
free path l and screening length xi) is found to be reduced below the Fermi
momentum by a factor of order l/L for shear fluctuations and (xi/L)^2 for
pressure fluctuations. The excitation of an elastic bending mode by the shear
fluctuations is estimated to fall within current experimental sensitivity for a
nanomechanical oscillator.
