How, exactly, does a jet engine make a plane go?
I'd also go along with the Wikipedia explanation. Remember Isaac Newton and "Force = Mass x Acceleration"? Well, integrate that once with respect to time and you get "Force x Time = Mass x Change in Velocity" or, to use the accepted terms, "Impulse = Change in Momentum".
Thus, if you have a device, such as a pure jet engine or, even better, a big by-pass turbofan, that gives a huge mass-flow of air an increase in momentum (backwards), the force that did that (backwards) is going to have an equal and opposite reaction forwards - which is the thrust of the engine.
Measure the speed of the jet plume and a relatively simple calculation will indicate the thrust. Equally, if you measure the thrust (say on a test rig), you can calculate the speed of the jet plume.