Newton’s Law and the propeller

Newton’s 3rd law of motion states “Every action has an equal and opposite reaction”

As the propeller spins, it sucks in air and pushes it out the back. This is the action and the reaction is the forward motion of the plane. Click to see a 400 Mb video



Propellers serve to push the plane forwards through the air. The propeller needs air in which to work and this is why propeller planes can not travel at high altitudes where the air is scarce. The propeller works in three specific ways to thrust the plane forwards.


Firstly, the shape of the propeller is such that it cork screws through the air. The cork screw motion pulls the propeller and the plane through the air.





Secondly, the propeller spins at high speeds pushing air back and thus pushing the plane forward. The more air that is pushed back the more the plane is pushed forward.


Thirdly, the propeller blades have a special aerofoil shape as shown on the right. The image on the right shows a cross section through the blade of a propeller. The blades are actually wings that spin around. The curved surface of the blades face the front of the plane and this creates a low pressure region in front of the plane sucking it forward.
Look at the special shape of a propeller from a model plane. Explain how the shape allows it to accomplish its function of thrusting the plane forwards.