Thrust's 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. Examples A fixed-wing aircraft generates forward thrust when air's pushed in the direction opposite to flight. This can be done in several ways including by the spinning blades of a propeller, or a rotating turbine pushing air from the back of a jet engine, or by ejecting… (More on Thrust)