How do I explain what makes an airplane fly to a non-technical person? As an engineer I can explain in very technical terms exactly what makes an airplane fly, however, it isn't easily understood by non-technical people.  How can I explain it to a non-technical person, or a nine year old, in a way that isn't really incorrect but is far less technical than what we learn as pilots?
The simplest explanation is the "hand out of the window" one:


  Hold your hand out of the window while in a moving car and hold your hand at an angle. It gets pushed upwards. Your hand represents the wing of an airplane. The plane's engine simply makes sure the "hand" keeps moving forward against the force of the wind.


Even a 4-year old understands the concept using this explanation.