Describe the purpose of a pneumatic actuator.

A pneumatic actuator is designed specifically to convert the energy stored in compressed air into mechanical motion. This conversion enables the actuator to perform various mechanical tasks, such as opening or closing valves, moving dampers, or driving other mechanical devices. The actuator uses the movement generated by the compressed air to produce linear or rotary motion, making it a crucial component in many automation and control systems where pneumatic power is preferred for its speed and reliability.

Understanding this function highlights why the other choices do not align with the primary role of a pneumatic actuator. Converting electrical energy into heat is associated with resistive heating elements, while transforming mechanical motion into fluid flow pertains more to pumps or fans. Controlling the pressure of a fluid is a characteristic of pressure regulators or control valves rather than an actuator itself. Therefore, the key purpose of a pneumatic actuator focuses on harnessing compressed air for mechanical action, affirming the correctness of the chosen answer.