Bulk modulus of the Femi gas show that the contribution of the kinetic energy to the bulk modulus of the electron gas at absolute zero is B = 1/3nmv2/F. It is convenient to use (6.60). We can use our result for B to find the velocity of sound, which in a compressible fluid is v = (B/p)^1/2, where v = (m/3M)^l/2 v_F, in agreement with (46). These estimates neglect attractive interactions.