Propulsion systems are technologies that enable vehicles, such as cars, airplanes, and rockets, to move. They work by generating thrust, which is the force that pushes the vehicle forward. Different types of propulsion systems include internal combustion engines, which burn fuel to create power, and electric motors, which use electricity to drive the vehicle. In the case of rockets, propulsion systems are designed to operate in space, where there is no air. These systems often use liquid or solid fuels to produce high-speed exhaust gases that propel the rocket upward. Overall, propulsion systems are essential for transportation and exploration in various environments.