Thrust is the force which moves a rocket through the air. Thrust
is generated by the rocket engine through the reaction of
accelerating a mass of gas. The gas is accelerated to the the
rear and the rocket is accelerated in the opposite direction. To
accelerate the gas, we need some kind of propulsion system. We
will discuss the details of various propulsion systems on some
other pages. For right now, let us just think of the propulsion
system as some machine which accelerates a gas. From Newton's
second law of motion, we can define a force to be the change in
momentum of an object with a change in time. Momentum is the
object's mass times the velocity. When dealing with a gas, the
basic thrust equation is given as: F = mdot e * Ve - mdot 0 * V0
+ (pe - p0) * Ae Thrust F is equal to the exit mass flow rate
mdot e times the exit velocity Ve minus the free stream mass
flow rate mdot 0 times the free stream velocity V0 plus the
pressure difference across the engine pe - p0 times the engine
area Ae. For liquid or