A propeller is a mechanical device that converts rotational motion into thrust, allowing vehicles like airplanes and boats to move through air or water. It consists of blades that spin around a central hub, creating a difference in pressure that pushes the vehicle forward. Propellers are commonly made from materials like metal or composite materials for durability and efficiency. In aviation, propellers are often found on small aircraft and helicopters, while in maritime contexts, they are used on ships and submarines. The design and size of a propeller can significantly affect performance, making it an essential component in the engineering of vehicles such as airplanes and boats.