  Magnetic stresses collimate protostellar winds into a common distribution of
force with angle. Sweeping into the ambient medium, such winds drive bipolar
molecular outflows whose properties are insensitive to the distribution of
ambient gas and to the details of how the wind is launched, and how its
intensity varies over time. Moreover, these properties are in accord with the
commonly observed features of outflows.
  This model is simple enough to permit a quantitative study of the feedback
effects from low-mass star formation. It predicts the rate at which
star-forming gas is ejected by winds, and hence the efficiency with which stars
form. Applied to individual star formation, it relates the stellar initial mass
function to the distribution of pre-stellar cores. Applied to cluster
formation, it indicates whether the resulting stellar system will remain
gravitationally bound.
  Using the energy injection and mass ejection implied by this model, we
investigate the dynamical evolution of a molecular clump as a stellar cluster
forms within it. This depends critically on the rate at which turbulence
decays: it may involve equilibrium star formation (slow decay), overstable
oscillations, or collapse (fast decay).
