What accelerates a missile or launch vehicle during liftoff?

During liftoff, a missile or launch vehicle is accelerated primarily by the thrust generated by its rocket engines. These engines combust propellant, producing high-pressure gases that are expelled downward, adhering to Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. Additionally, the vehicle’s design, including aerodynamic shaping, and the efficient use of fuel contribute to optimizing acceleration and minimizing drag during ascent.