Let’s count degrees of freedom.
Trains have one degree of freedom: they can move forward or backward along their longitudinal axis (1). They’re stuck on their line.
Cars have two degrees of freedom: they can move forward or backward along their longitudinal axis like a train (1) or rotate their longitudinal axis about their vertical axis (2), but they’re still stuck in the plane that’s wrapped around Earth.
Airplanes have 2-1/2 degrees of freedom: they can rotate their longitudinal axis around their vertical axis (1) or their lateral axis (2) and they can move forward along their longitudinal axis (2-1/2). They can’t move backward like a car or a train. They also can’t stop.
Helicopters have a full three degrees of freedom: up/down (1), left/right (2), or forward/back (3). Unlike all of the others, they don’t depend on motion to turn, and they don’t even depend on which direction their longitudinal axis is pointing. There is at least one thing that a helicopter has a hard time doing that an airplane does not (flying upside down), but that’s not nearly as cool as the ability to move in an arbitrary direction in space.
Because of this, I want a helicopter! Next time, we’ll consider my options for legally flying a helicopter and what I could do with it.