To understand this, we need to refer to the principles of aerodynamics. Aerodynamics is the branch of physics that deals with the study of dynamics air and it's relationship with solid bodies. Precisely, we must recall lift and resistance: lift is the aerodynamic force that acts perpendicular to the direction of the wind directed towards the aircraft in profile. The lift takes on a positive sign if it is upwardly oriented. The lift is generated by the difference the pressure between the top and bottom of the aircraft. The resistance, on the other hand, is that aerodynamic force that acts in the opposite direction and parallel to the aircraft.
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