We each have a unique voice because so many factors work together to produce that voice. As air passes over them, the vocal cords vibrate very quickly to produce sounds. <em>The higher the rate of vibration, called frequency, the higher the pitch will be.</em>
The direction of the electrical force is dependent upon whether the charged objects are charged with like charge or opposite charge and upon their spatial orientation. By knowing the type of charge on the two objects, the direction of the force on either one of them can be determined with a little reasoning.
The airplane engine uses oxygen from the air to keep the engines working. Rockets must carry their oxygen for the engines to operate. Third Law of Motion). Rocket propellants by combustion provide the hot gas es that produce reaction force (thrust) when ejected to the rear.