Final answer:
Jet engines propel aircraft forward without needing to push against anything, due to the expulsion of exhaust gases. Flywheels on piston engines even out vibrations by storing and releasing rotational inertia steadily. Jet turbines are designed to disintegrate safely in case of seizure, to prevent damage to the aircraft.
Step-by-step explanation:
The principle behind jet engines and rockets operates on Newton's Third Law of Motion: for every action, there is an equal and opposite reaction. When a jet engine expels exhaust gases forcefully to the rear, the reaction is that the engine, and thus the aircraft, is propelled forward. The exhaust gases do not need to push against anything; instead, the forward thrust is a reaction to the mass of the gases being ejected backward.
Regarding the flywheel on conventional piston engines, its primary effect is to smooth out the engine vibrations, which are caused by the alternating cycles of power strokes and inertial strokes of the individual pistons. The flywheel acts as a rotational inertia store, absorbing sudden torques and releasing energy more uniformly, thus maintaining a more steady rotational speed.
To ensure safety and protect the integrity of the aircraft, jet turbines are designed to mitigate the effects of sudden seizures. If a turbine seizes rapidly, rather than transferring angular momentum to the wing—which could cause severe damage or loss of the wing—the blades are made to detach or disintegrate in a controlled fashion, thus conserving angular momentum without impacting the wing's structure.