The ratio of thernal energy to momentum (Q/D) deposited in the solar wind by hydromagnetic waves is determined primarily by the wind and Alfv¿n speeds and by the rate of wave dissipation. When dissipation of Alfv¿n waves dominates, then Q/D=2(V+A). This restricts models for the possible acceleration of the solar wind by hydromagnetic waves. It also affects the manner in which resonant cosmic rays can interact with the solar wind and the interstellar medium.