Which device creates either rotary or linear motion when power is applied?

The device that creates either rotary or linear motion when power is applied is a solenoid actuator. Solenoid actuators convert electrical energy into linear motion through electromagnetic principles. When an electric current passes through the coil of the solenoid, it generates a magnetic field that moves a plunger or rod in a linear direction, thus creating motion.

While stepper motors and servo motors are designed for precise control of rotary motion, their primary function is to facilitate movement in a rotational capacity. Stepper motors move in discrete steps, allowing for the control of angular position and speed, whereas servo motors provide continuous rotation with feedback for precise positioning.

Pneumatic cylinders, on the other hand, utilize compressed air to generate linear motion. Although they also create linear movement, they do not operate based on electrical signals like solenoids do. This distinction emphasizes the solenoid actuator's role in producing linear motion directly from an electrical source, making it the correct answer.