Newton's Laws of Motion define the basic laws of mechanics, which we should be aware of when trying to understand the interaction between the air and aircraft. They can be stated as follows:

Newton's First Law: An object at rest or in motion will remain at rest or in motion at a constant speed, unless acted upon by an external force.

Newton's Second Law: A force is that which causes a change in momentum of a body. The rate of change of momentum is proportional to the force. When mass is constant, the net force is proportional to the acceleration (rate of change of velocity). Mathematically, this is F = ma

Newton's Third Law: When a force is applied from one body to another, there will be an equal and opposite reaction on the other body. 

Therefore, Newton's third law describes “action and reaction” - that when one force is applied, there is an equal and opposite force applied to the other body. For example, the aircraft applies a force to the air. In return, the air applies an opposite force on the aircraft (aerodynamic force).