Final answer:
The main purpose of the fuel jettison (dump) system in aircraft is to remove excess fuel in emergency situations, enabling a safe emergency landing by reducing the aircraft's weight.
Step-by-step explanation:
The purpose of the fuel jettison (dump) system and the jettison valve(s) in aircraft is primarily to remove excess fuel from the aircraft in emergency situations. If an aircraft needs to make an emergency landing shortly after takeoff, it may be too heavy with the full takeoff quantity of fuel to land safely. The jet fuel dump system allows it to quickly reduce weight to a safe landing weight. Jettisoning fuel is not related to normal operation control, preventing fuel leakage during refueling, or increasing fuel efficiency directly.
In relation to jet engines and rockets, the principle that describes their motion includes the expulsion of exhaust gases. The force that discharges the exhaust gases from the rear of the rocket generates a propulsive force in the opposite direction, pushing the rocket forward. It's important to note that the exhaust gases do not need to push against the surrounding air; they function effectively even in the vacuum of space.
Due to the ejection of the fuel gas, a rocket experiences a decrease in mass (dmg) and an increase in velocity (dui). Adding the momentum change for both the rocket and the exhaust gas results in the final momentum of the system. This follows the principle of conservation of momentum, which is central to the operation of propulsion systems.