For air-breathing jet engines, particularly turbofans, the actual exhaust velocity and the effective exhaust velocity are different by orders of magnitude.
2.
This allows a better match between the airspeed and the exhaust speed, which saves energy / propellant and enormously increases the effective exhaust velocity while reducing the actual exhaust velocity.
3.
Note that "'effective "'exhaust velocity and "'actual "'exhaust velocity can be significantly different, for example when a rocket is run within the atmosphere, atmospheric pressure on the outside of the engine causes a retarding force that reduces the specific impulse, and the effective exhaust velocity goes down, whereas the actual exhaust velocity is largely unaffected.
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