What Are Propellers Used For?
- For more specifics on how propellers push air or water in the opposite direction that you want to travel, examine Bernoulli's Principle and Newton's Third Law of Motion. The Third Law states that for every action there is an equal and opposite reaction. When the propeller exerts force onto the water or air, the water or air pushes back with equal force and propels the vessel forward. Bernoulli's Principle states that as the velocity of a fluid is increased, the pressure exerted by the fluid simultaneously decreases. The propellers cause the air or water behind the vessel to move fast and decrease the pressure of the air or water and allow the boat or plane to move forward.
- Boat propellers have various numbers of blades depending on how large the boat is and how fast the boat is designed to travel. Propellers for smaller boats are typically made up of at least three blades. Large boats can utilize the power of more than one propeller that contains up to five blades. These blades are attached to a central shaft much like the blades of a household fan. When the blades spin they create a pressure that accelerates the boat against the water.
- Airplanes typically have propellers with two or more blades. The blades are connected to the shaft by a hub. The blades of the propellers are in the shape of an airfoil, similar to the wings on an aircraft. The propellers are powered by the engine and give the plane lift during takeoff, and are essential to keeping the plane flying.
- Helicopters require two propellers to make it fly. One propeller is called the main rotor and is on the top of the helicopter. The main rotor produces thrust, redirecting the air downward and causing the helicopter to rise. The second rotor is found on the tail. This rotor helps propel the helicopter forward, backward and side-to-side. Both rotors work together to move the helicopter.
