After earning her doctorate, Morawetz spent a year as a research associate at MIT before returning to work as a research associate at the Courant Institute of Mathematical Sciences at NYU, for five more years. During this time she had no teaching requirements and could focus purely on research. She published work on a variety of topics in applied mathematics including viscosity, compressible fluids and transonic flows. Even if an aircraft remains subsonic, the air flowing around the wing can reach supersonic velocity. The mix of air at supersonic and subsonic velocity creates shock waves that can slow the airplane.