Thrust is the force which moves an craft from one point to another. Thrust is generated by the propulsion system of a given craft.

How is thrust generated?
Thrust is a mechanical force which is generated through the reaction of accelerating a mass of gas, as explained by Newton's third law of motion. A gas or working fluid is accelerated to the rear and the engine and aircraft are 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 F to be the change in momentum of an object with a change in time. Momentum is the object's mass m times the velocity V. So, between two times t1 and t2, the force is given by:

F = ((m * V)2 - (m * V)1) / (t2 - t1)

An Electric Ducted fan draws air in to a given duct via a fan system which utilizes an electric motor (like the DFR Rotocan) and expells air out of the oposite end at a grater speed. (from NASA web site)