Thrust is a reaction force described quantitatively by Newton's Second and Third Laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a proportional but opposite force on that system. The pushing or pulling force developed by an aircraft engine or a rocket engine. The force exerted in any direction by a fluid jet or by a powered screw, as, the thrust of an antitorque rotor. Specifically, in rocketry, \( F\,= m\cdot v\) where m is propellant mass flow and v is exhaust velocity relative to the vehicle. Also called momentum thrust.